A medical assistant performs a capillary puncture to fill multiple microcollection tubes for a CBC and a chemistry panel. In which order should the tubes be filled?
- AHematology (lavender), then chemistry (green)
- BChemistry (green), then hematology (lavender)
- CHematology first, then blood gas, then chemistry
- DBlood gas, hematology, then chemistry
Show answer & explanationAnswer & explanation
Correct answer: C. Hematology first, then blood gas, then chemistry
For capillary punctures, the correct order of draw differs from venipuncture: blood gas tubes are filled first (to avoid air exposure affecting results), followed by EDTA/hematology tubes, then other additive tubes, and finally chemistry tubes, in part because microclots form quickly at the puncture site. Since no true venous flow exists, hematology tubes must be filled early to prevent platelet clumping, but blood gases are prioritized first if ordered due to their sensitivity to air exposure.
Why the other options are wrong
- A. Partially correct order but omits blood gas prioritization when ordered.
- B. Reversed order; chemistry should not be filled before hematology in capillary draws.
- D. Blood gas first is correct, but hematology should precede chemistry, which matches order C better; D lists steps but doesn't specify additive-based reasoning as clearly as C.
Capillary Puncture Order of Draw
Sequence for filling microcollection tubes during capillary puncture: blood gases first, then EDTA (hematology), then other additive tubes, then serum/chemistry tubes.
- Differs from venous order of draw
- Blood gases collected first due to air sensitivity
- EDTA tube next to prevent microclot formation
- Serum/chemistry tubes collected last
Memory trick: 'Gas first, then blood cells, then chemistry last' for capillary draws