30+ Medical Terminology Abbreviations Every Medical Assistant Must Know (PRN, NPO, BID, STAT)

If you’ve ever stood next to a chart and thought “what does PRN mean?” — you’re not alone. Medical abbreviations are a foreign language at first, and the consequences of getting them wrong range from awkward to dangerous. A medication ordered “PRN” given as “TID” instead, or “NPO” patient given breakfast, can mean a real safety event. Whether you’re researching the what does prn mean in medical terminology for the first time or comparing programs, this guide pulls together what matters.

This post is a structured reference of the 30+ medical terminology abbreviations every medical assistant, patient care technician, and pharmacy technician must know cold. It’s organized by where you’ll see them — frequency abbreviations on the medication administration record, route abbreviations on the prescription, lab abbreviations on the chart, and the patient-status abbreviations clinicians use shorthand to communicate care.

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Frequency / Timing Abbreviations — What Does Prn Mean In Medical Terminology

These appear on prescriptions, MARs (Medication Administration Records), and orders:

Abbrev	Latin / Full	English meaning
PRN	pro re nata	As needed
STAT	statim	Immediately
AC	ante cibum	Before meals
PC	post cibum	After meals
HS	hora somni	At bedtime
QD ⚠️	quaque die	Once daily (now discouraged — use “daily”)
BID	bis in die	Twice daily
TID	ter in die	Three times daily
QID	quater in die	Four times daily
Q4H / Q6H / Q8H	quaque 4 horas	Every 4/6/8 hours
QOD ⚠️	quaque alta die	Every other day (discouraged — use “every other day”)

Notes:

• QD and QOD appear on the Joint Commission’s “Do Not Use” list because handwriting can confuse them with QID and other abbreviations. Most modern EHR systems block them, and you should write “daily” or “every other day” instead.
• PRN orders should always include a reason (“PRN for pain >5/10”) and a maximum frequency (“max Q4H”).

Route of Administration Abbreviations

These tell you HOW a medication is given:

Abbrev	Meaning
PO	By mouth (per os)
IV	Intravenous
IM	Intramuscular
SC / SubQ	Subcutaneous
PR	Per rectum
SL	Sublingual (under the tongue)
IN	Intranasal
TOP	Topical
OD ⚠️	Right eye (discouraged — use “right eye”)
OS ⚠️	Left eye (discouraged — use “left eye”)
OU ⚠️	Both eyes (discouraged — use “both eyes”)
AD ⚠️	Right ear (discouraged — use “right ear”)
AS ⚠️	Left ear (discouraged — use “left ear”)

The eye/ear abbreviations are also Joint Commission “Do Not Use” because OD/OS can be confused with each other. You’ll still see them on legacy orders, but new prescriptions should spell them out.

Patient Status Abbreviations

You’ll see these in chart notes, handoffs, and during rounds:

Abbrev	Meaning
NPO	Nothing by mouth (nil per os)
NKDA	No known drug allergies
NKA	No known allergies
DNR	Do not resuscitate
DNI	Do not intubate
AMA	Against medical advice
CC	Chief complaint
HPI	History of present illness
PMH	Past medical history
ROS	Review of systems
PT	Patient (or sometimes physical therapy — context-dependent)
R/O	Rule out
W/U	Workup
DC	Discharge (or discontinue — context-dependent)
SOB	Shortness of breath
N/V	Nausea/vomiting
CP	Chest pain
HA	Headache

NPO is the highest-stakes one for medical assistants and PCTs to know — a patient ordered NPO before surgery cannot eat or drink anything (sometimes including water and oral medications) without delaying their procedure or putting them at aspiration risk.

Common Lab Abbreviations

The labs you’ll see ordered most often:

Abbrev	What it stands for	What it measures
CBC	Complete blood count	RBC, WBC, hemoglobin, hematocrit, platelets
BMP	Basic metabolic panel	Glucose, BUN, creatinine, electrolytes
CMP	Comprehensive metabolic panel	BMP + liver enzymes + protein + albumin
HbA1c	Glycated hemoglobin	3-month average blood glucose (diabetes)
PT/INR	Prothrombin time / international normalized ratio	Coagulation status — warfarin monitoring
PTT	Partial thromboplastin time	Coagulation — heparin monitoring
TSH	Thyroid stimulating hormone	Thyroid function
UA	Urinalysis	Urine chemistry + microscopy
C&S	Culture and sensitivity	Identifies bacteria + antibiotic susceptibility
LFT	Liver function test	ALT, AST, alkaline phosphatase, bilirubin
Lipid panel	—	Total cholesterol, HDL, LDL, triglycerides
EKG / ECG	Electrocardiogram	Heart electrical activity

Diagnosis-Related Shorthand

Quick pattern-recognition shorthand for common conditions:

Abbrev	Meaning
HTN	Hypertension
HLD	Hyperlipidemia
DM (or DM2)	Diabetes mellitus (type 2)
CAD	Coronary artery disease
CHF	Congestive heart failure
COPD	Chronic obstructive pulmonary disease
CVA	Cerebrovascular accident (stroke)
MI	Myocardial infarction (heart attack)
DVT	Deep vein thrombosis
PE	Pulmonary embolism
UTI	Urinary tract infection
URI	Upper respiratory infection
GERD	Gastroesophageal reflux disease
ESRD	End-stage renal disease
CKD	Chronic kidney disease

Vital Signs Abbreviations

What you’ll see on the vitals chart:

Abbrev	Meaning
BP	Blood pressure
HR (or P)	Heart rate (or pulse)
RR	Respiratory rate
T	Temperature
SpO2	Pulse oximetry (oxygen saturation)
WT / Wt	Weight
Ht	Height
BMI	Body mass index

Procedure / Setting Abbreviations

Abbrev	Meaning
OR	Operating room
ER / ED	Emergency room / department
ICU	Intensive care unit
CCU	Cardiac/coronary care unit
PACU	Post-anesthesia care unit
L&D	Labor and delivery
NICU	Neonatal intensive care unit
PICU	Pediatric intensive care unit
OPD	Outpatient department
OB/GYN	Obstetrics/gynecology

How to Memorize Medical Terminology — and What’s Actually Tested

The 30+ abbreviations above show up on the NHA CCMA exam, the NHA CPCT/A exam, and the PTCB exam at high frequency. The most testable patterns:

1. Frequency abbreviations + their max safe combinations. “Acetaminophen 500 mg PO Q4H PRN max 4g/day” — every part of that string matters.
2. Route + drug compatibility. Some drugs can be IV but not IM (e.g., diazepam IV is preferred). Some are PO-only.
3. NPO timing before surgery. Typically NPO after midnight, but newer ERAS (Enhanced Recovery After Surgery) protocols allow clear liquids up to 2 hours pre-op.
4. DNR/DNI distinction. Patients can be DNR (no CPR, no defibrillation) but still want intubation for reversible respiratory failure.
5. Lab → diagnosis pairing. Knowing CBC for infection, BMP for kidney/electrolyte, HbA1c for diabetes management.

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Frequently Asked Questions

What does PRN mean in medical terminology?

PRN comes from the Latin “pro re nata” and means “as needed.” A PRN medication is given only when a specific condition is met — typically pain, nausea, or anxiety — within a maximum frequency limit (e.g., “every 4 hours as needed”).

What does NPO mean?

NPO comes from “nil per os” (Latin for “nothing by mouth”). An NPO patient cannot eat or drink anything — typically before surgery, certain procedures, or with certain GI conditions. The order may include exceptions (e.g., “NPO except medications with sips of water”).

What does BID mean?

BID comes from “bis in die” and means “twice daily.” Medications ordered BID are typically given every 12 hours (e.g., 8 AM and 8 PM).

What does STAT mean in medical terminology?

STAT comes from the Latin “statim” and means “immediately.” A STAT order should be carried out as soon as possible, typically within 15-30 minutes for medications and within 60 minutes for non-emergency labs.

What does CVA mean?

CVA stands for “cerebrovascular accident” — a stroke. CVAs are classified as ischemic (blocked vessel, ~85% of cases) or hemorrhagic (bleeding into the brain, ~15%). The treatment differs significantly between the two types.

What does TID mean?

TID comes from “ter in die” and means “three times daily.” Medications ordered TID are typically given every 8 hours (e.g., 8 AM, 4 PM, 12 AM) or with meals.

Is QD an acceptable medical abbreviation?

QD (“once daily”) is on the Joint Commission’s “Do Not Use” list because of risk of confusion with QID or other abbreviations in handwritten orders. Modern EHR systems block QD; write “daily” instead.

What does q4h mean?

q4h means “every 4 hours” — the dose is given on a 4-hour schedule (e.g., 6 AM, 10 AM, 2 PM, 6 PM, 10 PM, 2 AM). Other variants: q6h (every 6 hours), q8h (every 8 hours), q12h (every 12 hours, also written BID).

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Source: U.S. Bureau of Labor Statistics — Healthcare Occupations