Certified Medical Assistant (CMA AAMA)Procedures, Examinations and DiagnosticsHard
A medical assistant is drawing a coagulation study and must fill a light blue-top tube. Why is it essential that this tube be filled to its exact volume mark?
- ATo maintain the correct 9:1 ratio of blood to sodium citrate anticoagulant
- BTo ensure enough serum separates during centrifugation
- CTo prevent glycolysis from falsely lowering glucose results
- DTo prevent hemoconcentration from a prolonged tourniquet application
Show answer & explanationAnswer & explanation
Correct answer: A. To maintain the correct 9:1 ratio of blood to sodium citrate anticoagulant
Light blue-top tubes contain sodium citrate anticoagulant in a fixed volume, and they must be filled completely to maintain the correct 9:1 blood-to-anticoagulant ratio; underfilling causes an excess of citrate relative to blood, which can falsely prolong coagulation results such as PT/PTT.
Why the other options are wrong
- B. Serum separation applies to serum tubes, not sodium citrate (plasma) tubes.
- C. Glycolysis concerns relate to gray-top glucose tubes, not coagulation tubes.
- D. Hemoconcentration relates to tourniquet time, not tube fill volume.
Sodium Citrate Ratio (Light Blue-Top)
Light blue-top tubes must be filled to the exact volume mark to maintain the required 9:1 ratio of blood to sodium citrate anticoagulant for accurate coagulation testing.
- 9:1 blood-to-citrate ratio required
- Underfilling causes falsely prolonged PT/PTT results
- Used for coagulation studies like PT and PTT
Memory trick: '9 parts blood, 1 part citrate — fill it right or throw a fit'