NHA Certified Clinical Medical Assistant (CCMA)Foundational Knowledge and Basic ScienceMedium
A medical assistant is preparing to administer an intramuscular (IM) injection to an adult patient. Which of the following needle gauges is most appropriate for this procedure?
- A25-gauge
- B18-gauge
- C21-gauge
- D27-gauge
Show answer & explanationAnswer & explanation
Correct answer: C. 21-gauge
For most adult intramuscular injections, a 21- to 23-gauge needle is appropriate. A 21-gauge needle balances ease of administration with patient comfort and medication viscosity.
Why the other options are wrong
- A. 25-gauge is commonly used for subcutaneous injections or some IM injections in children/thin adults.
- B. 18-gauge is a large gauge, typically used for drawing up viscous medications or for IV access, not routine IM injections.
- D. 27-gauge is typically used for intradermal injections.
IM Needle Gauge
The gauge of a needle for intramuscular injections in adults typically ranges from 21 to 23, providing a balance for medication delivery and patient comfort.
- Gauge indicates needle lumen diameter (higher gauge = smaller diameter)
- Length depends on site and patient's muscle mass
- Viscosity of medication influences gauge choice
Memory trick: Small numbers, big holes; big numbers, small roles.