Which of the following is an acceptable sample for a prothrombin ...

[fbq8i]

Which of the following is an acceptable sample for a prothrombin time (PT) test?
 
  a. One that was collected 22 hours before testing and stored at room temperature
  b. One with a very small clot that was easily removed
  c. 3.2 Sodium citrate blood sample immediately collected following a serum separator tube
  d. Blood anticoagulated with heparin and brought to the laboratory within 1 hour

Question 2

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

[bblaney]

Answer to Question 1

ANS: A
PT specimens may be held 18 to 24C (room temperature) for 24 hours from the time of collection and still give valid results. Any clot in a specimen makes the sample useless for coagulation testing. Serum separator tubes contain a clot activator; this can contaminate the next tube drawn, and, for coagulation, is the same as having a clot. Heparinized samples are not used for coagulation testing.

Answer to Question 2

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.