Which of the following will cause spuriously prolonged clot-based coagulation tests?

a. An evacuated 3.2% sodium citrate tube filled to 50% capacity
b. An evacuated 3.2% sodium citrate tube filled to 90% capacity
c. Prolonged tourniquet application
d. Plasma collected from a traumatic tap

ANS: A
Filling an evacuated 3.2% sodium citrate only halfway (50%) will lead to falsely prolonged clot-based coagulation test results. The relative excess anticoagulant will bind (some) of the calcium added in the test system. A 90% fill gives valid results and can be used. Prolonged tourniquet application and plasma collected from a traumatic tap both have the potential of activating coagulation, thus leading to shortened, not prolonged, results.