Abbreviations, Acronyms, and Plural Forms
Abbreviations in context
Abbreviations work as symbols, so learn the convention along with the letters: vital signs (BP, HR, RR, T), laboratory tests (CBC, WBC, RBC, Hgb, Hct, BUN, Na, K), imaging (MRI, CT, US), routes (PO by mouth, PR by rectum, IM, IV, SQ), frequencies (BID, TID, QID, q.d., q.h.s., PRN, STAT), timing (AC before meals, PC after meals), and charting shorthand (H&P, ROS, Dx, Tx, Hx, s/p). Some are acronyms pronounced as words (AIDS, HIPAA); others are initialisms read letter by letter (CBC).
Plural rules
The ending reveals the language of origin:
- -a becomes -ae: vertebra to vertebrae, bursa to bursae
- -is becomes -es: diagnosis to diagnoses, anastomosis to anastomoses
- -us becomes -i: bronchus to bronchi, calculus to calculi (but virus to viruses)
- -um becomes -a: septum to septa, diverticulum to diverticula
- -on becomes -a: ganglion to ganglia
- -x becomes -ces: apex to apices, thorax to thoraces; phalanx to phalanges
- -y becomes -ies: biopsy to biopsies
Traps
Do not add -s to abbreviated units; "three RBCs" is chart shorthand, not a formal plural. Watch ambiguous abbreviations - MS, SOB, and DOE each carry several meanings. The dangerous pair q.d. (daily) and QID (four times daily) is a classic error source, and trailing periods are increasingly dropped.
Rule of thumb
If a singular ends in -us, try -i; if it ends in -is, try -es; if it ends in -um or -on, try -a. Some terms have been fully anglicized and accept an English plural, so check a dictionary rather than guessing.