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AMA-11 Abbreviations and the Goldilocks' Principle: Getting the Mix Just Right

Abbreviations and The AMA Manual of Style

Abbreviations are very common in medical writing, so knowing conventions for using them is a valuable skill for authors and editors. Among the many industry-standard writing style guides, The AMA Manual of Style (AMA-11) is the go-to guide for authors who write or edit medical manuscripts. This post focuses on AMA-11 guidelines for using abbreviations, as well as some tips to help authors avoid errors related to abbreviations. While many of the preferences here reflect AMA-11 style, many of these tips and preferences are universal to all scientific writing.


Why use abbreviations? At the heart of scientific and medical manuscripts are an immense number of lengthy technical terms that can appear repeatedly throughout a text. By converting these terms to an abbreviated form, valuable print space is saved and the length of a document is shortened, which is a major concern in scientific publications. Also, because authors of scientific and medical writing are communicating with readers who share very technical and specialized background knowledge from a specific field of study, they use abbreviations to quickly summarize and communicate complex processes that their readers understand. Abbreviations also improve readability by avoiding repetition of long cumbersome technical terms throughout a manuscript. Considering these benefits, within each field of study, a number of common terms are abbreviated.


There are three forms of shortened words. An abbreviation is a form of a shortened term that formed by using a few letters from the original term. Some examples include, Dr: doctor, Chem: Chemistry, wt: weight, no: number, org: organization, dept: department, admin: administration, and bldg: building. Acronyms are abbreviations formed from the initial letters of each consecutive word in a compound word; acronyms are pronounced as words and not pronounced letter by letter. Some examples include, AIDS, HEPA, UNESCO, SARS, MRSA, ELISA, GABA, and BLAST. Initialisms are abbreviations also formed from the initial letters of each consecutive word in a compound word, yet unlike acronyms, initialisms are pronounced letter by letter; Examples include, DNA, CDC, WHO, UN, FDA, USA, EU, UV.


Only use an abbreviated term if you mention the term 3 times in a text. If a term is mentioned less than 3 times, use the fully spelled out form of the term (aka, fully expanded and defined form) without abbreviating.  When a term is repeated 3 or more times in a text, consider abbreviating the term. Some style guides recommend only using an abbreviated term after mentioning a term at least 5 times, yet AMA-11 sets the limit at 3 mentions. When using an abbreviation for the first time in a text, spell out the complete and expanded word form that the abbreviation represents, and then follow this with the abbreviation in parenthesis, as in this example:


              Abnormally elevated serum low-density lipoprotein cholesterol (LDL-C) is major health concern as it plays a central role in the pathogenesis of atherosclerosis and cardiovascular disease.


On the second mention of the term, the abbreviation can standalone:


              Serum LDL-C is considered a primary predictive measure of cardiovascular event risk.


When an abbreviation is more well-known that the spelled out form, reverse the order on first mention: name the abbreviation first followed by the spelled out term in parentheses.


              Funding was provided by UNESCO (The United Nations Educational, Scientific and

Cultural Organization)


              A new SIM (Subscriber Identity Module) card is needed.



AMA-11 Guidelines for Abbreviations


Make acronyms plural by adding a lowercase “s” letter. Some authors mistakenly add a possessive marker in such case, but this is incorrect.


                   Correct: RCTs


                   Incorrect: RCT’s


Singular and plural forms of acronyms are commonly used together in manuscripts. AMA-11 recommends that whichever form is used first in the text, should be spelled out only once.  


Avoid introducing abbreviations in a title or beginning a sentence with one. Recast the sentence if necessary.


AMA-11 calls for repeating the complete and expanded word form followed by the acronym in parentheses in several places of a manuscript, including the abstract, in the body of the text, and in all tables and figures. If you introduce an abbreviations in the beginning of a manuscript but don’t mention it much until later in the text, you can also help your reader by defining and providing the fully expanded form of the abbreviation again.


Abbreviations from AMA-11


Sample abbreviations for common medical terms from AMA-11:             


              acute myocardial infarction



              absolute risk reduction



              body mass index



              bone marrow transplantation



              Cardiovascular disease



              clustered regularly interspaced short palindromic repeats



              methicillin-resistant Staphylococcus aureus



              quality of life



              single-nucleotide variant



              tumor, node, metastasis staging system



              Vascular endothelial growth factor


As shown in the list above, most clinical, technical medical terms in AMA-11 are capitalized, yet some abbreviations include a combination of lowercase and capital letters.



              hepatitis B surface antigen



              complementary DNA



              transfer RNA



              quantitative real-time PCR



For a more comprehensive list of common clinical, technical medical terms, see Chapter 13 of AMA-11.



Sample of common SI units of measurement


Quantitative values in scientific manuscripts typically follow the International System of Units, referred to as SI units, including base units and derived units. Most abbreviations of SI units are not capitalized, unless they are derived from proper nouns and some other exceptions. One exception is the term liter, which is capitalized as L to avoid being confused with lower case l and the number 1.


Examples of SI base units


Time: s for second; min for minute; h for hour 


Mass: kg for kilogram


Amount of a substance: mol for mole


Volume: L for liter


Examples of derived SI units:


Density, mass density: kg/m3  for kilogram per cubic meter


Concentration: mol/m3   for mole per cubic meter


Area: m2          for square meter


Volume:           m3  for cubic meter


SI units of time (day, hour, millisecond, minute, month, second, week, and year) should not be abbreviated when used in text, except for in virgule and parenthetical constructions, as well as in tables, figures, and as shown below:In-text use of SI units of measurement:


              Correct: Patients were monitored for 30 days.

              Incorrect: Patients were monitored for 30 d.


In tables and figures, SI units of time are abbreviated to save space, but they should be defined in a footnote, typically below the table or figure.


Examples of abbreviated SI units of time in virgule and parenthetical constructions.


             At this dosage (900 mg/d for 10 wk) all patients experienced improvements.

(parenthetical construction)


             The dosage was increased to 20 mg/d.  (virgule construction)          


For SI units of time, do not add an “s” to make them plural.        

Correct: 10 min


              Incorrect: 10 mins



              Correct: 2 h


              Incorrect: 2 hs

Some abbreviations are accompanied by superscripted letters or numbers.



              hemoglobin A1c



              forced expiratory flow, midexpiratory phase



              drug half-life


Do not punctuate abbreviations.


              Correct:  2 h at room temperature


              Incorrect: 2 h. at room temperature



              Correct: Dr Johnson


              Incorrect: Dr. Johnson



              Correct: US holidays


              Incorrect: U.S. holidays



              Correct: vs


              Incorrect: vs.

              Correct: eg


              Incorrect: e.g.

              Correct: ie


              Incorrect: i.e.



              Correct: MD


              Incorrect: M.D.


              Correct: PhD


              Incorrect: PhD.



However these abbreviations are punctuated:


         No. (for number)


              St. (for street)


              Et al.




Some authors do not like the AMA-11 preference for no punctuation with eg and ie, and instead they use the more conventional punctuated e.g. and i.e. Most journals will allow authors to choose one style or another, but they do ask that you be consistent. So whatever style you use  don’t use eg and e.g. in same text. Use one style or the other.


Following AMA-11, some well-known abbreviations do not need to be spelled out and defined.


              AIDS    acquired immunodeficiency syndrome


              CI    confidence interval


              COVID-19   coronavirus disease 2019


              DNA    deoxyribonucleic acid


              HIV      human immunodeficiency virus


              IQR     interquartile range


              OR      odds ratio


              SEM    standard error of the mean


              vs        versus



Some AMA-11 abbreviations are italicized.




                   P = 0.05


In a health care delivery context, certain abbreviations should never be used as they have been misread, with harmful or fatal outcomes for patients, including, bid, npo, prn, etc. See The Joint Commission on Accreditation of Healthcare Organizations for more examples:



While the convention is to italicize non-English terms, at this point, certain Latin-based abbreviations are well-known and used so frequently in scientific writing that they are not italicized:


              Incorrect: in situ, in vivo, ex vivo, in vitro, in silico


              Correct: in situ, in vivo, ex vivo, in vitro, in silico


The same follows for these Latin-based terms:


              Incorrect: eg, ie, et al., vs, etc.


              Correct: eg, ie, et al., vs, etc.



Tips for effectively using abbreviations

·       While abbreviations effectively summarize lengthy terms, when overused, they can make the text a confusing “alphabet soup” and tax the memory of your readers struggling to recall what multiple abbreviations mean. Finding just the right balance is key to effectively using abbreviations. Apply a Goldilocks’ principle: not too many, not too few. Knowing your audience (readers) is helpful in finding this balance. As a general rule, use abbreviations when they reduce the print space or word count or when they improve ease of reading.



·       Use abbreviations consistently. For example, if you are using a singular version of an acronym (RBC) but occasionally refer to the plural version (RBCs), be careful with subject verb agreement. Add a plural “s” marker to an acronym to make the acronym plural and use the correct verb that agrees with a plural subject.


Incorrect: RBC were collected.


                 Correct: RBCs were collected.


Pay attention to acronyms that are referred to multiple times in the text in their plural form (RBCs) and singular form (RBC). In this scenario, sometimes authors mistakenly use a plural form when a singular form is called for, and vice versa.


                   Incorrect: NSAID are known for effectively treating inflammation.


                    Correct: NSAIDs are known for effectively treating inflammation.

Also identify whether an abbreviation is for an adjective or a noun. Sometimes an abbreviation can have an adjective and a noun form, as in the adjective multi-drug resistant (MDR) and the noun multi-drug resistance (MDR). Sometimes authors may mistakenly use an adjective acronym as if it were a noun. Pay attention to when an abbreviation is an adjective that needs to be followed by noun.


                Incorrect: It was identified as an MDR.

(adjective as initialism for multi-drug resistant)


                Correct: It was identified as an MDR bacteria.

(adjective as initialism for multi-drug resistant)


                 Correct: MDR is antimicrobial resistance shown by a species of microorganism to at  least one antimicrobial drug in three or more antimicrobial categories.

                     (noun initialism for multi-drug resistance)


Finally, do not add a noun after an abbreviation that already includes the noun in the abbreviation. Notice this case in the example below where the initialism WHO stands for World Health Organization. It is redundant to add the term organization after WHO.


                        Incorrect: The WHO organization approved this measure


                        Correct: The WHO approved this measure.


·       If English is not your first language, pay attention to the order of letters in abbreviations. For example, the term colony forming units is abbreviated as CFU, but for authors of whose native language is Spanish, Portuguese, French, Italian, the order of this term and the initialism is inverted to UFC. You will need  to carefully edit your use of abbreviations because such errors may not be easily noticed during the writing process.


                       unità formanti colonie UFC (Italian)


                       unidades formadoras de colonias UFC (Spanish)


                      unidades formadoras de colônias (Portuguese)


                        unités formant des colonies UFC (French)


·      For authors whose first language is not English, knowing which indefinite article (a/an) is used before an abbreviation can be challenging. Yet the choice is based on the pronunciation of the abbreviation. Vowels as well as some consonants (h, m, n, r, s) when pronounced as an open sound (the mouth is continuously open when pronouncing) are preceded by the indefinite article an, whereas consonants are generally closed sounds, so they are preceded by the definite article, a. In some cases, you will need to pay attention to whether the abbreviation is pronounced as a single word as in an acronym, or if each letter is pronounced, as in an initialism. For example the term SARS-CoV-2 is pronounced as a word, and the first sound of this word is a closed sound, so it is preceded by the article a, as in a SARS-CoV-2 diagnosis. However, for the acronym STD, each letter is pronounced, and the first letter makes an open sound, so it is preceded by the indefinite article an, as in an STD. This may be a challenging set of rules to consider, so you can easily checkout Merriam-Webster’s Online Dictionary if you are in doubt about what article precedes a noun. Note some examples below.


                   An ICU

                            An EMT

                            An EMR

                            An OTC drug  



                            An HMO

                            An MD

                            An MRI

                            An NDA

                            An NSAID

                            An RCT

                            An SAE



                            A MRSA outbreak

                            A NAFLD diagnosis

                            A CPR training

                            A PCR test

                            A QALY


·    If an acronym is capitalized, don’t assume that the fully spelled out term should be capitalized. Only capitalize acronyms that are proper nouns, and use lowercase letters for common nouns. Many authors unknowingly follow this practice, so edit carefully for this issue. Ultimately, too many capitalized terms has a similar effect as too many acronyms: they clutter the text with information that impedes ease of reading. So catching this issue will improve readability of your text.


                   Correct: emergency medical technician (EMT)


                     Incorrect: Emergency Medical Technician (EMT)



                   Correct: area under the curve (AUC)


                            Incorrect: Area Under the Curve (AUC)



                            Correct: atherosclerotic cardiovascular disease (ASCVD)


                            Incorrect: Atherosclerotic Cardiovascular Disease (ASCVD)



                            Correct: doctor of surgery (DCh)


                            Incorrect: Doctor of Surgery (DCh)



·      If you have a high number of abbreviations in a long text, consider listing them in a table at the end of the document to help your readers easily access them.


·      Be careful about the abbreviation style you choose. It’s always best to follow a well-known industry-standard style guidebook such as AMA-11 than to follow the style preferences found in various articles you may be citing. For example, you can search Google or even PubMed and find research papers that use a variety nonstandard abbreviation forms.


·      If you are submitting an article for publication to a journal, check the journal’s guidelines’ for authors page. A journal’s guidelines for using abbreviations sometimes differ from AMA-11 style. Ultimately, it is best to defer to the style preferences of the journal if you plan to publish with them. Some journals dedicated to a specific medical specialty will not require authors to expand certain acronyms that they consider to be well-known by their readers. For example, journals dedicated to cardiology may not require well-known abbreviations to be spelled out, as in the following acronyms:










·      Be flexible with these general rules on abbreviations. For example, while some style guides and journals discourage using abbreviations in abstracts and titles, in some cases, an abstract would be improved by using an acronym, especially when a long cumbersome term is repeated several times in the abstract and if spelling out the term would surpass the word count limit for the abstract. For example, using the acronym GM-CSF repeatedly in an abstract makes more sense than repeatedly spelling out a lengthy term like granulocyte-macrophage colony-stimulating factor. You will lower the word count this way, save print space, and improve readability. Likewise, it is generally recommended to not use acronyms in titles, but it is acceptable to use an acronym when the title is very long and acronym replaces a lengthy term.


One other example of being flexible with these abbreviation rules includes the AMA-11         preference for not abbreviating units of time (second, hour, day, etc.) in the body of the text except for tables, figures, and parenthetical or virgule constructions. Yet, in the material and method section of a paper, other style guides will recommend abbreviating SI time units to be brief and save space.


         This is not a comprehensive review of the AMA-11 chapter on abbreviations. You will   find more information in the manual on topics such as abbreviations of journal articles, author names, institutions and locations named in journal article bylines.

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