Use (or not) of appostrohe when making an abbreviated plural

Question

We had a discussion the other day that needs settling. I am a medical student and in our "industry" we use a lot of three letter abbreviations such as: CPR (Cardiac Pulmonary Resuscitation), PUN (Patient Unmet Need), PEN (Practitioner Educational Need) etc. You get the message. Now, the other day our tutor wrote in a presentation: PENs, PUNs, CPRs and I argued (who am I to argue with the tutor?) that it should be PEN's, PUN's CPR's as we are pluralising an abbreviation. What is the rule (if any) about pluralising abbreviations? Dan

Answer 1

Both conventions are used in different contexts, and I've seen a lot of instances of both.

Although this Wikipedia article is not an authoritative reference, it does contain links to references.

There is a question about how to pluralize acronyms. Often a writer will add an 's' following an apostrophe, as in "PC's". However, Kate Turabian, writing about style in academic writings,[50] allows for an apostrophe to form plural acronyms "only when an abbreviation contains internal periods or both capital and lowercase letters". Turabian would therefore prefer "DVDs" and "URLs" and "Ph.D.'s". The Modern Language Association[51] and American Psychological Association[52][53] prohibit apostrophes from being used to pluralize acronyms regardless of periods (so "compact discs" would be "CDs" or "C.D.s"), whereas the New York Times style guide requires an apostrophe when pluralizing all abbreviations regardless of periods (preferring "PC's, TV's and VCR's").[54]

Possessive plurals that also include apostrophes for mere pluralization and periods appear especially complex: for example, the C.D.'s' labels (the labels of the compact discs). In some instances, however, an apostrophe may increase clarity: for example, if the final letter of an abbreviation is S, as in SOS's (although abbreviations ending with S can also take -es, e.g. SOSes), or when pluralizing an abbreviation that has periods.[55][56]