Certified Medical Assistant (CMA AAMA)Procedures, Examinations and DiagnosticsEasy
A medical assistant is performing a venipuncture using multiple evacuated tubes. Which tube should be collected first if no blood culture is ordered?
- AGreen-top (heparin) tube
- BLavender-top (EDTA) tube
- CGray-top (sodium fluoride) tube
- DLight blue-top (sodium citrate) tube
Show answer & explanationAnswer & explanation
Correct answer: D. Light blue-top (sodium citrate) tube
When a blood culture is not ordered, the light blue (citrate) tube is drawn first because coagulation studies are extremely sensitive to tissue thromboplastin contamination from a previous tube's additive carryover.
Why the other options are wrong
- A. Heparin tubes are drawn after citrate and serum tubes.
- B. EDTA is drawn after citrate tubes.
- C. Gray-top fluoride tubes are drawn near the end of the order.
Order of Draw
The standardized CLSI sequence for collecting blood tubes to prevent additive carryover from affecting test results.
- Sequence: blood culture, light blue citrate, red/SST serum, green heparin, lavender EDTA, gray fluoride
- Citrate tube is first non-culture tube due to coagulation sensitivity
- Additive carryover can falsely alter clotting, electrolyte, or glucose results
Memory trick: 'Stop Light Red-Green-Purple-Gray' for Culture, Light blue, Red, Green, Purple, Gray