Abbreviations, acronyms and symbols

An abbreviation saves the writer space and costs the reader a lookup. Whether the trade is worth making turns on how often a term recurs, how many other abbreviations crowd the text, whether the letters already mean something else, where the reader will find the definition and, in dosing instructions, whether a misreading could harm a patient. The kinds of shortening, the symbols a field uses and the abbreviation etc. each raise their own questions.

Kinds of shortening

An abbreviation is a shortened word or phrase that represents the whole and usually consists of the most identifiable letters of the word it refers to, so hour, minute and second become hr, min and sec, and professor becomes Prof. ¹ Abbreviation is the containing class: every acronym is an abbreviation, but not every abbreviation is an acronym. ^{2, 3, 1, 4} An acronym is pronounced as a word, as NATO, NIMBY, RICE and PAINBASE are, while an initialism is pronounced letter by letter, as FDA, AMA and BP are. ^{3, 4, 5} Acronyms spell words or other felicitous-sounding terms, such as RANKL. ² In everyday conversation, all these shortened forms are often called acronyms. ³ Acro- is a word element meaning high and -nym one meaning name, so an acronym is a name a little higher in the lexical hierarchy than an initialism. ⁵

Another definition draws the line by formation. ⁶ An acronym is formed from the first letter or first few letters of each word in a phrase, as sonar is from sound navigation and ranging and Benelux from Belgium, the Netherlands and Luxembourg, while an abbreviation may be any shortened form, including words with the middle omitted, such as Rd for Road. ⁶ The AMA Manual of Style calls a term formed from initial letters and pronounced as a separate word an initialism. ⁶

Sorted by how they are formed, abbreviations fall into these kinds: ¹

• Initialisms, also called alphabetisms or sigla, are formed, usually, from the first letter or letters of the words of a phrase and pronounced letter by letter, as NIH and ALS. Many internet and texting abbreviations are initialisms.
• Acronyms are initialisms pronounced as words, as AIDS or LVAD.
• Partial acronyms, or syllabic abbreviations, combine initial syllables, as Medtronic from medicine and electronic, or MEDLINE.
• Second-order abbreviations contain other abbreviations, as RBD for REM behavioural disorder.
• Backronyms fit words to existing letters, as EQUATOR for Enhancing the QUAlity and Transparency Of health Research. They can seem contrived when the words have to be bent to fit.
• Shortenings, or truncations, keep the first letters, as flu and lab and the Latin eg and ie. The less common apheresis keeps the end, as phone.
• Contractions keep the first and last letters or mark the omission with an apostrophe, as Mr, HTN and can't.
• Blendings, or portmanteaus, merge two words, as endorphin, genome and vitamin.
• Mnemonic devices look like abbreviations without being them, as SPICED-T for the elements of a clinical research article's title: setting, patients, intervention, comparator, endpoint, design and sometimes time.

¹

Abbreviations comprise, among others, initialisms, acronyms, symbols and measurements such as mg, dL, yd and sec. ⁵ A mnemonic is a way to remember things, such as EGBDF for the lines of a musical score. ⁵ PAINBASE, for the elements of a pain care plan, may also qualify as an acrostic because its vertical letters are expanded with words, although the acrostics one usage writer had seen were laid out as a square. ⁵ Many mnemonics are also acronyms, such as AIDS, MEDLARS and MEDLINE. ⁵

APGAR is both a mnemonic and an acronym, devised as a mnemonic by L. Joseph Butterfield of Children's Hospital in Denver for appearance, pulse, grimace, activity and respiration; these criteria are less discrete and explanatory than the score's actual criteria, which the medical and nursing dictionaries give. ⁵ Another account classes the same letters as a backronym for the assessment criteria of the score named after its developer, Virginia Apgar. ¹

The most-used initialism in the world is OK, believed to be a short form of "Oll Korrect", which most likely came from a fad of comical misspellings in an 1838 satirical article; the longest partial acronym appears to be the 22-letter US Navy term ADCOMSUBORDCOMPHIBSPAC; and the 58-letter Welsh place name Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch is shortened to Llanfairpwll. ¹

Abbreviations can also be sorted by the community that uses them: ⁶

• across general society, such as FYI and FAQ
• across the medical and scientific community, for therapeutic areas such as CNS, CV and OB-GYN, diseases and their measurements such as AML, MS, HIV, HbA1c and LFT, frequencies such as BID, QD and QID, which may or may not separate each letter with a period, and diagnostic technologies such as PET and CAT scans
• in a regulatory context, such as FDA, EMA, EudraCT and PMDA
• across the pharmaceutical industry, such as NDA, IND, ISS, ISE, ICH and CTD
• within a particular company, including the names of research programmes, some of which do not even match their letters

⁶

There are no universal standards of use, either across institutions or in the rules of usage. ⁶ Institutions differ in the term itself: clinical study report against clinical trial report, an institutional review board in the USA against an ethics committee in Europe and a research ethics board in Canada, and an investigational new drug application in the USA against a clinical trial application in Europe and Canada for documents that serve the same purpose under different names and structures. ⁶ The rules of usage are inconsistent: a multiple-letter abbreviation formed from a single word generally takes no periods, so television is TV, yet postscript is often written P.S. ⁶ Although there is much conformance in structure under the ICH common technical document, nations and languages still differ in how abbreviations and acronyms are accepted and used, and the variation often forces the creation of multiple documents for multiple authorities where a single universal document should suffice. ⁷

History and spread

Writers have long shortened words, usually because the medium of the time imposed limits of space, time or cost. ⁸ Written abbreviations were first used when authors had to chip words into stone or write with ink on scarce parchment, and they continue in text messaging on small screens. ⁹ Egyptian scribes began abbreviating hieroglyphs into the cursive hieratic script, better suited to papyrus, about 3000 BCE; most Roman stone inscriptions had at least one abbreviation, and some abbreviations had more than one meaning and caused so much confusion that Emperor Justinian passed a law regulating their use, and the standard 1899 work on Latin abbreviations lists more than 14,000; Old English turned "and" into "&" and "the" into "ye"; medieval manuscripts, shaped by the price of parchment and the labour of copying, need a dictionary for their abbreviations alone; and the telegraph in the United States in the 1840s gave abbreviations such as POTUS. ⁸ Abbreviations have also been used to avoid mentioning a sacred name, as magical symbols in alchemy and the occult, as language-independent marks understood in multilingual societies, and to promote memory and recognition. ¹⁰ Acronyms and initialisms apply the acrophonic principle, by which a letter takes its value from the first sound of its name, as a from aleph, so that coronary artery bypass grafting becomes CABG and blood pressure BP. ⁸

Acronyms date back almost as far as abbreviations, but their widespread use is a twentieth-century phenomenon that began with the World Wars, with early military examples such as AWOL, POW, HQ and SNAFU; common examples include RADAR, LASER and AIDS. ^{9, 8} In the Second World War, soldiers wrote to their sweethearts in abbreviations to thwart censors and enemy agents, which shows that abbreviations can prevent communication as well as facilitate it. ⁸ Acronyms have become so accepted that capitalisation and punctuation are often dropped and many users do not know what the initials originally indicated, and abbreviations are also used orally within groups, to communicate rapidly with colleagues who use the same terms. ⁹

Clinical trials are increasingly named with acronyms, as MRFIT for the Multiple Risk Factor Intervention Trial: in 2002 nearly 4,200 cardiology trials were named with acronyms, and a 2015 survey identified 47 SMART, 40 HEART and 16 HOPE trials. ⁸ Publications from trials named with acronyms are cited twice as often as those without and tend to be accepted by higher-ranking journals, acronyms with positive connotations, such as SMART and ASPIRE, do better than those with negative ones, such as OUCH and BEWARE, and the connotation can affect patient recruitment. ⁸

Abbreviations permeate industry, science and culture in the United States, which abbreviates the names of states, journals, elements, airports, units, months and days, government agencies, academic degrees and military ranks among much else. ¹⁰ The AMA Manual of Style has an 88-page chapter listing abbreviations and 98 index entries on them; in March 2019 Barnes & Noble listed 433 books on abbreviations and Google retrieved 196 million web hits for the term; the online Oxford Dictionary of Abbreviations holds more than 100,000 abbreviations and acronyms with more than a million definitions, and Acronym Finder more than 5 million. ¹⁰ New abbreviations are introduced faster than they can be added to dictionaries, and English uses more abbreviations than any other language. ¹⁰ Yet after hundreds of thousands of abbreviations created over 5,000 years, the conclusion is that they should be used sparingly. ¹⁰

Whether to abbreviate

Abbreviations are shortened words or phrases that make writing easier, the text shorter and reading faster by reducing the need to repeat a longer word or phrase, so that maximum left arterial dimension from a right parasternal short-axis heart-base view can be shortened to LAmax. ¹⁰ They speed writing, shorten text, may aid recall and can be pronounced with fewer syllables, but they are now so plentiful that they often make reading difficult. ¹¹ Their gains in efficiency are often offset by reduced comprehension: carefully crafted abbreviations can markedly improve communication, but unknown ones can confuse and divide readers, and unintended ones can have embarrassing consequences. ¹²

Inserting an abbreviation into a sentence obliges the reader to backtrack and commit the term to memory, and where the only other occurrence comes several paragraphs later the reader may well have forgotten it and must go back through the text or to the list of abbreviations. ¹³ So an abbreviation should be worth the reader's while: the term abbreviated should be used often enough for readers to learn what it stands for, or be one they probably already recognise, and be long enough for the expanded term to be disruptive, as beclometasone dipropionate (BDP) is. ¹³ Abbreviations can also be very helpful in improving the flow of a text, particularly where they result in an acronym, such as MedDRA. ¹³

Every abbreviation sets the writer's convenience against the reader's courtesy, and the more a text is abbreviated for the writer's convenience, the more it risks the discourtesy of confusing readers; skilfully used, abbreviations can provide both. ¹⁰ Whether one is effective depends on how likely the primary and secondary audiences are to know it, how often it is used, how many different abbreviations the document uses, how close together they sit, and where in the document they appear — text, captions, titles or abstracts. ^{12, 10, 14}

Abbreviations should be used only when they appear often enough to be useful. ¹⁵ Many journals require a term to be used at least five times in an article before it is abbreviated, with the catch that a long term may be used four times in one paragraph and never again. ¹⁵ One writer's rules of thumb are to use an abbreviation or acronym only if it replaces a very long term, such as ethylenediaminetetraacetic acid (EDTA), and is used more than once; if it is used more than ten times in an article or publication; and if it replaces more than one word, since shortening diabetes to DB is not helpful. ⁹

The basic rules for using abbreviations are widely accepted, if not always followed. ¹⁴ On when to use them, check whether the publisher allows or prohibits particular abbreviations; consider a shortening instead, as the Joint Commission for the Joint Commission on Accreditation of Healthcare Organizations; use abbreviations only where their meaning is clear and they avoid annoying repetition; use them sparingly; and use only common abbreviations whose meanings are readily available in standard references. ¹⁵ The APA manual recommends defining any abbreviation Merriam-Webster's Collegiate Dictionary designates as abbrev., and using those without the designation undefined, a criterion that, one writer notes, may not be appropriate in medicine. ¹⁵

One review describes nine common problems with abbreviations, most of which argue for using them sparingly. ¹² An abbreviation can be superfluous, saving no words yet still needing to be decoded, as HD and OS have the same word count as high-dose and osteosarcoma. ¹¹ It can be hard to read as either a word or letters, as LVPWT, ASCVD and CTEPH are. ¹¹ It can be coined by the authors, as PNDWH and PPDWH for people newly and previously diagnosed with HIV, and a related problem is labelling experimental groups A, B and C rather than responders, nonresponders and controls. ¹¹ An abbreviation unique to a specific document should never be created, the exception perhaps being a proposal that a field adopt a new term or nomenclature. ¹⁶ And a name or phrase can be created without considering how it will inevitably be abbreviated, with embarrassing implications, as for the South Lake Union Trolley, the Department of Urban and Metropolitan Planning and the Duke University Marching Band. ¹⁷ The other five problems are abbreviations that are undefined, whose definition cannot be found, that are ambiguous, that pile up in a sentence and that are misunderstood. ^{11, 17}

An abbreviation can also be unnecessary because the term already contains one: miR for microRNA abbreviates a term in which RNA is already an abbreviation. ¹⁸

The decision is easy in a document that uses no more than about five common abbreviations for long terms that are used often. ¹⁹ In practice, the skilful use of abbreviations requires judgement informed by a knowledge of their strengths and weaknesses, and much depends on the assumptions made about the primary and secondary audiences, the number and location of terms that can be abbreviated, and how often they might be used. ¹⁹ The best advice is to put courtesy before convenience. ¹⁹

Too many abbreviations

Acronyms and other abbreviations are overused, a habit known as alphabet soup: they should be used judiciously to aid comprehension, kept where possible to a limited number of well-known ones, and unusual ones used only where necessary to avoid repeating long multiword terms. ^{4, 20} Text overloaded with abbreviations is difficult to read, especially if they are not well known. ²⁰

Although counter-intuitive to many writers, having more abbreviations makes a text more difficult, not easier, to understand, because abbreviations often make the reader go back and search for definitions. ²¹ Abbreviations make abstracts impossible to understand, so abstracts crammed full of them are best ignored when choosing abstracts from PubMed to rewrite as an exercise, and an abstract about troublesome words repeated the phrase rather than abbreviating it to TW. ²² Even familiar abbreviations can be annoying when there are too many in a sentence, a condition called abbrevobabble, as in "Prognostic Value of LGE-CMR in HCM". ¹¹ Overuse of acronyms can make whole sections of text impossible to understand. ²³

One editor concluded that if the abbreviations and acronyms of clinical development language and medical publications are a problem for medically educated people, they must be one for a lay audience: at the end of an investigator meeting, a Danish investigator congratulating the organisers added that the participants could not really follow all the acronyms. ²³ Acronyms and abbreviations do not always translate into other languages and are not obvious to foreigners. ^{23, 7} The well-known Polish acronym of a technical institute, NOT, meant nothing to an English speaker in Warsaw who spoke no Polish, and he read a note reading NOT Czacki Street, written for a taxi driver, as naming the one street he should not go to. ²³

A parody of overuse appeared in the New England Journal of Medicine in 1989. ²³ A letter complains of a recent trend (RT) in the medical literature (ML) to abbreviate previously unabbreviated phrases for the sake of efficiency (PUPSAE), noting that although it makes good sense (GS), the frequency with which it is used can tax the inexperienced reader (IR), and that sometimes repetition can actually be beneficial (RCABB) by allowing the reader to retain words he does not constantly have to refer back to (WOHCREBT). ²³ The editor's reply, in the same register, allows some previously abbreviated phrases (PAPS) in widespread use (WU), and occasionally PUPSAE when repeatedly spelling them out would be unusually cumbersome (STOWBUC), while admitting that all of it often raises the reader's and the editor's blood pressure and heart rate. ²⁴

As the vectors of communication press writers to convey concepts in fewer characters, and where speed is of the essence, writers tend to fall back on these time-and-space savers, yet their use may result in message confusion and longer elapsed time, because the recipient has to work out what the sender meant. ⁶ Their use has become so ubiquitous that users are often unaware of the source term, and asked what the letters stand for, too often respond with a blank stare and a shrug. ⁶ A necropsy report notation, MDYPPT, meant obviously moderate dark yellow precipitate to the technician who wrote it, and a road sign reading S.I. Thwy Nxt Rt did not intuitively mean Staten Island Thruway Next Right even for a native speaker. ⁷ One writer who changed jobs within the industry sat through his first meeting at the new company completely baffled by the abbreviations and acronyms. ⁷

Undefined abbreviations deprive readers of essential information and can become codes that separate groups who know their meaning from groups who do not. ¹¹ Their use has been called admission into a secret society comprising only the cognoscenti. ⁶ Acronyms and abbreviations have also been defined as a code designed to keep out the uninitiated, which is counterproductive for communication because it ostracises readers outside the club. ⁹ Heavy use of abbreviations can discourage readers in one discipline from reading articles in other disciplines. ¹¹

Spoken use is, in one experienced writer's judgement, more confusing than written, because accent, pronunciation and letters that sound alike, such as c and k, do not allow a clear association between the letter and its source word. ⁷ The same writer holds that the use of abbreviations and acronyms often represents arrogance on the native speaker's part, the assumption that anyone competent and reasonably intelligent should readily understand the secret code. ⁷

Abbreviations and acronyms quickly become jargon. ⁷ Fowler's Modern English Usage classifies them as curtailed words, some of which establish themselves so fully as to take the place of their originals or make them seem pedantic, while others remain slangy or suited only to particular audiences; combining initial letters, it observes, became so popular, especially in America, that the word acronym was coined for it. ⁶ The editors of the AMA's scientific publications discourage abbreviations, acronyms and initialisms in their journals except for internationally approved units of measure and some well-recognised clinical, technical and general terms and symbols, because overuse can be confusing and ambiguous for readers, especially those of another culture or outside a specific specialty, while allowing that, since abbreviations save space, they may be acceptable where the original words are repeated numerous times. ⁶ Selective use also has the support of one experienced writer, who finds few advantages in unbridled use, because the space saved is quickly outweighed by the potential for confusion and misinterpretation, which increase the time to comprehension, and who, as long as journal articles and regulatory filings are less driven by saving space and time, would reserve frequent use for media that are space-restricted, such as tweets. ²⁵

Abbreviations also remove the meaning from the phrase they represent. ⁹ The World Health Organization changed female circumcision to female genital mutilation expressly to include the word mutilation and underscore the appalling nature of the practice, and the now widespread FGM removes that effect and makes the term anodyne again. ⁹

One view goes further: with the almost ubiquitous use of computers and word processing, there is no need for abbreviations and acronyms, they should be discouraged, and the instructions to authors of nearly all scientific journals tell authors to use them sparingly. ⁹ On this view, spelling them out adds only a few words to a manuscript, especially if other verbiage is cut, and abbreviations and acronyms do not help the reader to understand a text but detract from communication. ⁹

Abbreviations with more than one meaning

The same letters can stand for different organisations, documents, conditions or measures: AMWA for the American Medical Writers Association or the American Medical Women's Association, CSR for a clinical study report or a cumulative survival rate, and AUC for drug exposure under a concentration–time curve in pharmacokinetics or for discriminative performance under a receiver operating characteristic curve in prognostic modelling. ^{26, 27, 28}

AMWA can also stand for many other organisations, among them the Australian Medical Writers Association, and TD, chosen at random, carries many meanings inside medicine and out, from tardive dyskinesia and tetanus–diphtheria vaccination to touchdown; similar tables can be made from almost any combination of two letters. ^{29, 30} Even in the same context, otherwise common abbreviations can be ambiguous: in cardiology, TVP can mean tricuspid valve plasty, tricuspid valve prolapse, temporary transvenous pacing or transplant vasculopathy. ¹¹ There are only 17,000 three-letter acronyms. ³¹

Take care that an abbreviation is not more commonly known as something else. ¹³ A company abbreviated its study endpoint pre-defined event to PDE in the protocol for a drug that was a phosphodiesterase (PDE) inhibitor, with the result that the protocol was incomprehensible. ¹³ A website of medical abbreviations shows how many terms can be expanded from one abbreviation: VTE can stand for venous thromboembolism, ventricular tachycardia event or vicarious trial and error, the first two equally valid in cardiology. ¹³ As a guide, writers should ask whether the abbreviation improves the readability of the text, whether it is commonly known to mean something else, and whether it can be misunderstood; an abbreviation that does not improve readability and can be misunderstood should not be used. ¹³

One abbreviation can carry two or more contradictory or ambiguous meanings, which can create dangerous miscommunication, and Neil M. Davis published a partial list of such abbreviations to sensitise health practitioners and medical editors to the problem. ^{32, 33}

Anatomy. APC is advanced pancreatic or advanced prostate cancer; BCa bladder or breast cancer; BO bowel obstruction or bowel open; CAS carotid artery stenosis, cerebral arteriosclerosis or coronary artery stenosis; CLD chronic liver or chronic lung disease; ESLD end-stage liver or end-stage lung disease; LF left foot, little finger or long finger; LKT laparoscopic kidney transplantation or liver–kidney transplantation; LL left leg, left lung, lower lid, lower limb or lower lip; LNE lymph node enlargement or lymph node excision; LT liver or lung transplantation, and Ltx liver or lung transplant; OLB open-liver or open-lung biopsy; OPC operable pancreatic carcinoma, oropharyngeal cancer or oropharyngeal candidiasis; PAA popliteal or pulmonary artery aneurysm; PBL primary brain or primary breast lymphoma; SCCP small cell carcinoma of the prostate or squamous cell carcinoma of the penis; TSCC thymic, tongue or tonsillar squamous cell carcinoma; HAO hand or hip osteoarthritis; HO hand or hip orthosis; IAI intra-abdominal infection or intra-abdominal injury; LVO left ventricular opacification, output or overactivity; WBRT whole-brain or whole-breast radiotherapy; IBC invasive bladder or invasive breast cancer; ICA internal carotid artery, intracranial abscess or intracranial aneurysm; LAPC locally advanced pancreatic or prostatic cancer; MBC male or metastatic breast cancer; MPM malignant peritoneal or pleural mesothelioma; and NBM no bowel movement, normal bowel movement or nothing by mouth. ^{34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61}

Drug names. GEM is gemcitabine or gemfibrozil; DNR did not respond, do not report or do not resuscitate; AMI amifostine or amitriptyline; ATR atracurium or atropine; KET ketamine or ketoconazole; DW deionised water, dextrose in water or distilled water; AZT azathioprine or azidothymidine (zidovudine); DX dexamethasone, dexmedetomidine or dextromethorphan; CLOF clofarabine or clofazimine; MTZ mirtazapine or mitoxantrone; CPM chlorpheniramine maleate or cyclophosphamide; NITRO nitroglycerin or sodium nitroprusside; CPZ chlorpromazine or Compazine; PBZ phenoxybenzamine, phenylbutazone or pyribenzamine; TMZ temazepam or temozolomide; and Pit Pitocin or Pitressin. Regimen acronyms each expand to different combinations: FEC is fluorouracil, epirubicin and cyclophosphamide or fluorouracil, etoposide and cisplatin; VAD is vincristine, doxorubicin (Adriamycin) and dactinomycin or vincristine, doxorubicin (Adriamycin) and dexamethasone; VAC, VAP and TAC each stand for several vincristine-based combinations; and TAC also means a tetracaine, adrenaline and cocaine solution or triamcinolone cream. ^{62, 63, 64, 65, 66, 67, 68, 69, 70, 71}

Diseases, symptoms and conditions. EOP is early-onset Parkinsonism, pneumonia, preeclampsia or psychosis; ADVT acute or asymptomatic deep venous thrombosis; IRDM insulin-required or insulin-resistant diabetes mellitus; GD Gaucher disease or Graves' disease; IRF impaired renal function or improvement in renal function; ED eating disorder, elbow disarticulation, emotional disorder or erectile dysfunction; HCC hepatocellular or Hurthle cell carcinoma; MS mitral stenosis or multiple sclerosis; EIH environmentally induced hyperthermia, exercise-induced hypertension, exercise-induced hyperthermia or exercise-induced hypoxaemia; HD Hansen, Hodgkin or Huntington disease; PD Paget disease, panic disorder, Parkinson disease, personality disorder or Peyronie disease; IAD incontinent associated dermatitis or intractable atopic dermatitis; PHTN portal hypertension, prehypertension or pulmonary hypertension; RM radical mastectomy or reduction mammoplasty; RTI reproductive or respiratory tract infection; PVO peripheral vascular, portal vein or pulmonary venous occlusion; and SAD seasonal affective disorder or social anxiety disorder. ^{72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82}

Miscellaneous. IT is intrathecal, intratracheal, intratumoural or intratympanic; ABP ambulatory or arterial blood pressure; AQoL Acne, Assessment of, Asthma-related or Australian Quality of Life; LAM laminectomy, laparoscopic-assisted myomectomy or laser-assisted myringotomy; LFD lactose-free, low-fat or low-fibre diet; BR bright red or brown; LHSH long-handled shoehorn or long-handled shower head; ERT enzyme or estrogen replacement therapy; Mon Monday or month; FSW female sex worker or field service worker; MV manual or mechanical ventilation; I & D incision and drainage or irrigation and debridement; TBA to be absorbed, added, administered, admitted, announced, arranged or assessed; T/E the testosterone-to-epitestosterone or testosterone-to-estrogen ratio or the trunk-to-extremity skinfold thickness index; NABS no active or normoactive bowel sounds; SDBP seated, standing or supine diastolic blood pressure; NE no effect, no enlargement or not evaluated; SGAs second-generation antihistamines or antipsychotics; Tx therapist, therapy, traction, transcription, transfer, transfuse, transplant, transplantation or treatment; PORT postoperative radiotherapy, postoperative respiratory therapy or prostate-only radiotherapy; SSE saline solution or soapsuds enema; S & S swish and spit or swish and swallow; STF special or standard tube feeding; and SA suicide alert or suicide attempt. ^{83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100}

Patient care units. PCU is a palliative, primary, progressive or protective care unit; ACU an acute receiving unit or an ambulatory care unit; IPCU an inpatient palliative care unit, an intensive paediatric care unit or an intensive psychiatric care unit; and TICU a thoracic, transplant or trauma intensive care unit. ^{101, 102, 103}

Syndromes. RS is Raynaud, Reiter, Rett, Reye or Richter syndrome; SJS Schwartz-Jampel, Stevens-Johnson or Swyer-James syndrome; TS Tay-Sachs disease, Tourette syndrome or Turner syndrome; and WS Waardenburg, Warner, West or Williams syndrome. ^{104, 105, 106}

An examination of the list shows that these abbreviations do not communicate with any certainty and present possible dangers to the health of patients. ¹⁰⁷

An internationally recognised list giving each abbreviation one meaning would need all the medical specialties, allied health professionals, health organisations and government agencies to agree; an international health organisation would have to create and maintain it and arbitrate between submitted meanings, such as PT for physical therapy, prothrombin time, preterm, parathyroid, patellar tendon, patient and phototoxicity; and health professionals could not realistically be expected to honour a distinction between PT, pt. and Pt. ^{108, 109} Such an effort would take hundreds of thousands of hours, the list would need maintaining as new abbreviations were proposed, a worldwide version would meet the different structure of the Romance languages, in which HIV is VIH, and a European edition might be needed for differences in spelling. ^{109, 32} Disallowing abbreviations would be very difficult to introduce and enforce: health personnel have used them daily throughout their careers; some have become word-like, such as rehab, exam, info, DNA, AIDS, MRI, ICU, DNR, the days of the week and months of the year, mL and kg, among hundreds more; and they save the writer's and reader's time, save space, decrease misspellings and make it easier to fit information into a form or table. ¹¹⁰

Before inventing a new abbreviation, researchers and authors must question whether it is necessary, and must not create one already in common use or with a contradictory or ambiguous meaning, checking with common sense or with comprehensive, up-to-date resources such as PubMed, medical abbreviation books and websites. ¹¹¹ Where possible, avoid abbreviating drug names, abbreviate syndromes with great care, and be sensitive to single letters that stand for more than one organ or state: B for breast, brain, blood or bladder; L for liver or lung; P for pancreas or prostate; H for hand or hip; R for renal or respiratory; C for cerebral, coronary or carotid; N for no or normal; S for special or standard; and O for open or obstructed. ¹¹¹ Medical editors reviewing manuscripts must make sure they do not introduce contradictory, ambiguous and dangerous abbreviations into the health vocabulary. ¹¹¹ There is hope that artificial intelligence, voice recognition and future products can supply further workable solutions. ¹¹¹

Abbreviations in dosing instructions

There are no good reasons for using prescription abbreviations in a regulatory document: nobody in the pharmaceutical industry is writing a prescription, and a protocol must give clear instructions about what to do and when. ¹³ It is irrelevant whether the writer knows that t.i.d. stands for ter in die; what matters is that other people understand it to mean what the writer thinks it means. ¹³ QD is read as once daily or as four times daily depending on the country the reader works in and what they have been told, which makes it a fourfold overdose waiting to happen and the reason never to use it in any document other than a prescription. ¹³ If typing once daily or daily is tiresome, the autocorrect can be set to do it. ¹³ Prescription abbreviations in regulatory documents can also lead to sloppy language such as bd dosage and the American q12 for twice daily, and there are no prizes for the writer who uses the most abbreviations. ¹³

The use of abbreviations is a glaring danger spot in the prescribing and administration of medication. ¹¹² Many physicians create their own abbreviations, which are difficult or impossible for anyone else to decipher, and even standard abbreviations can be hard to resolve because many have several meanings: among the 13 meanings of OD that Davis's Medical Abbreviations lists are once daily and right eye, and Davis notes a case in which Lugol's solution (iodine) was placed in a patient's right eye by mistake. ¹¹²

In a study of 643,000 medication errors, 30,000 (4.7%) were attributable to abbreviations — IJ for injection was read as IV, a dose written as .X mg was read as X mg, which is why the leading zero of 0.X mg is preferred, and q1d for daily was mistaken for q.i.d. — and a further 11,800 abbreviations were not analysed because their meanings could not be determined. ¹⁷ In a one-day review of 255 patient charts in six Canadian hospitals, almost a third of patients had medication orders containing abbreviations dangerous enough to be on a do-not-use list. ¹⁷

The US Joint Commission, which accredits health care institutions, requires accredited organisations to develop a do-not-use list of dangerous abbreviations, to avoid the medical errors that misunderstood abbreviations have caused. ^{113, 9} Davis calls it a step in the right direction that does not completely solve the systemic problem of the numerous abbreviations with dangerous contradictory or ambiguous meanings. ¹¹³ Many medical terms share the same abbreviation or acronym, with consequences for patient safety, and the Health Quality Council of Alberta runs a website whose slogan is that writing it out can save a life. ⁹

After a dosing regimen in a protocol was mistyped as q.i.d. instead of b.i.d., the lesson drawn was to spell it out when in doubt: twice daily (b.i.d.), four times daily (q.i.d.). ¹¹⁴

Defining an abbreviation

The conventional way is to define an abbreviation in parentheses at first mention and use it thereafter in most circumstances. ^{115, 116} An abbreviation so common that, in context, a definition is unnecessary, as DNA and HIV are, can go undefined, but when in doubt it should be defined. ¹¹⁶ No rule appears to require a term to be abbreviated, and several abbreviations may be used without definition: DNA, RNA, HIV, CD as in CD4, DSM-V, ICD-10, EDTA, PaO2, PaCO2, SPSS and TNM stage. ¹⁴ Another view is that every abbreviation used must be defined. ¹¹¹ Readers who feel insulted by having to read the definition of an abbreviation they already know should get over it. ¹¹ Expanding the letters can still leave a reader facing an unfamiliar medical word, as with electrocardiogram, because an expansion alone does not supply the meaning that a definition does. ³

When defining an abbreviation, put the most common or recognisable element first: continuous positive airway pressure (CPAP), but NSAID (nonsteroidal anti-inflammatory drug). ¹¹⁶ Writers spelling out an acronym frequently capitalise the expansion, as in Acquired Immunodeficiency Syndrome (AIDS), when it takes no initial capitals. ⁵ Once defined, use the abbreviation throughout the rest of the text, except to begin a sentence and in figures and tables, whose captions and titles define it again so that readers need not consult the text. ¹¹⁶ One writer would also make a case for spelling out the full term occasionally after it has been defined, as in a scientific article's conclusions, and for redefining it at the beginning of long reports or long sections, such as each chapter of a book. ¹¹⁶ For documents that are long or use several abbreviations, include a list of abbreviations at the beginning if the format allows. ¹¹⁶ There is no formal rule about whether the abbreviation or its explanation comes first, and the applicable style guide settles it. ¹¹⁷ An abbreviation would not normally be explained in a conclusion. ¹¹⁷

Readers can fail to find the definition: in shorter documents expansion at first mention can be sufficient, but in longer documents, or where many abbreviations are used in different parts of the text, searching for the definition can be frustrating, time-consuming and unsuccessful. ¹¹ One argument against the first-use rule is that it only makes sense if a document is read from the first page, since a reader who starts anywhere else risks missing the first use and cannot find out what the abbreviation means. ¹¹⁸ Most competent medical writers include a list of abbreviations at the start of a document so that the meaning can be found from anywhere in it, yet most still spend much quality-control and editing time searching for and defining every abbreviation at a first use that will change with the next review cycle. ¹¹⁸ The suggestion that follows is to direct any client or author who asks for first-use definitions to the list at the start of the document, since first use is then the same for every abbreviation: it is the list. ¹¹⁸

Another practice keeps both: a list of acronyms and abbreviations early in documents such as protocols and study reports, which is now standard practice and especially valuable where the terminology is esoteric, and a spelled-out term at first use, after which the bare form is acceptable. ⁷ Relying on a list has a cost: people looking for information outside their own domain have to look up strings of letters in a list of definitions, if there is one, back at the beginning of an article, and so constantly interrupt their reading. ⁹

An editor of a paper on metabolic syndrome found the author writing "the MS", as in "children have the MS", apparently to keep it distinct from multiple sclerosis, and asked what the appropriate frame for an abbreviation is: if the article is about metabolic syndrome, can MS be used freely, or is the frame one branch of medicine, or all of medicine? ¹¹⁹ The editor would not use JAMA anywhere in medicine if it meant the Journal of Asian Martial Arts. ¹²⁰

Even after a first-mention definition, a casual reader might turn to a later page, see MS, and wonder what multiple sclerosis has to do with an article about metabolic syndrome. ¹¹⁵ One practice is to spell out and abbreviate at first mention and thereafter simply write "the syndrome", and in a piece running over many pages to use the full two-word phrase again on the third or fourth page, MS on the next few pages, and so on alternately to the end, so that no reader has to flip back to the beginning to recall what MS stands for. ^{115, 121} Another convention, usually in journals' instructions to authors, is that an author who uses many abbreviations provides a short glossary at the top of the first page. ¹²¹ Multiple sclerosis is not usually thought of or referred to as a syndrome and is not listed among syndromes in either Dorland's or Stedman's dictionary. ¹²¹

No abbreviation should be used in a title or abstract unless it is defined, because the body of the text will not appear in an abstracting service. ¹¹¹ Another rule is not to use or define abbreviations in titles and headings unless their meaning is unambiguous in context without a definition, and never to use an abbreviation as a heading's only term. ¹⁶ The American Chemical Society's ACS Style Guide advises writers to avoid abbreviations in the title of a paper. ¹⁶

A definition can be spoken as well as written. ²⁵ Anyone attending a meeting where some participants may not know company-specific abbreviations is encouraged to define the terms deliberately when using them in conversation, and decoder sheets prepared for new employees make them more comfortable with the culture of their new environment and spare them the embarrassment of asking for a translation. ²⁵

An abbreviation in its sentence

Do not begin a sentence with an abbreviation, although this rule is not practical in many life-science topics. ¹⁶ The indefinite article before an abbreviation is chosen by how the abbreviation is pronounced, not by whether its first letter is a consonant or a vowel, so it is a scientific development plan but an SDP, and an NYU student, never a NYU student. ^{13, 20} A SDP disrupts the flow of the text because the reader reads the abbreviation as ess dee pee. ¹³ ZP is acceptable as the abbreviation for both the singular zona pellucida and the plural zonae pellucidae, even within a single manuscript on human embryos whose sentences sometimes deal with more than one. ^{122, 123, 124}

An abbreviation is sometimes followed by a noun that is already part of the expanded term: a writer who introduces DMEM for Dulbecco's modified Eagle's medium should not later write DMEM medium, nor SAD disorder after introducing SAD for seasonal affective disorder. ¹²⁵ These instances can be found by searching globally for each abbreviation and looking for a repetitive word nearby. ¹²⁵

Pharmacokinetic symbols

Pharmacokinetic symbols should convey their meaning to the reader immediately and precisely. ¹²⁶ Many PK parameters raid the Greek alphabet: tau (τ) represents the dosing interval, so AUCτ denotes the area under the plasma concentration–time curve over a dosing interval. ¹²⁶ Rate constants follow chemical engineering in using k, often with a subscript, giving kel for elimination and ka for absorption, and kel may be reported as λz to show that it was derived from the terminal portion of the concentration–time curve. ¹²⁶ The area under the curve from time zero to infinity can be written as AUC, AUC∞, AUC0–∞ or AUC0→∞, and all are correct. ¹²⁶ Several published papers have proposed a gold standard for PK symbols without any being universally accepted; the core symbol for a parameter tends to be similar whatever its origin, and the discrepancies lie in the subscripts; and the many EMA and FDA guidances on pharmacokinetics define no symbols. ¹²⁶ The medical writer's task is to keep PK symbols consistent within a project, so that data can be compared across clinical studies and extrapolated back to preclinical work. ¹²⁶

Etc. and the incomplete list

Etc. is a contraction of the Latin et cetera, "and the rest; and similar things", and indicates that a list is incomplete. ¹²⁷ Its use relies on the reader having a good idea of what completes the list: a vet who treats small domestic animals such as dogs, cats and rabbits can reasonably be assumed to treat hamsters, gerbils and guinea pigs too. ¹²⁷ Where readers have no idea what completes a list, as with a research site said to have projects in family studies, community, enhancement, commercialisation and so on, misuse of etc. gives the impression that the writer could not be bothered and can leave the reader feeling ignorant and frustrated. ¹²⁷

Combining etc. with including is unnecessary, because including already indicates that the list is not comprehensive. ¹²⁷ Authors quite commonly write including and then list everything, which is fine in American English but not generally accepted in British English. ¹²⁷ A series of dots in place of etc. is a device used to let the reader imagine what happened next, but in medical writing the reader should be reading what comes next, not imagining it. ¹²⁷