To ensure the best possible specimen, carefully follow collection requirements. Adherence to these
guidelines will improve coagulation study results.
- Patient should be fasting, if possible. For certain tests, the patient cannot be receiving anticoagulant
medication (heparin or warfarin/Coumadin).
- Draw blood from the patient into light blue-top (sodium citrate) evacuated tubes containing 3.2%
a. If the patient’s hematocrit is <25% or >55%, the volume of anticoagulant in the tube should be
adjusted. Use the following formula to determine the correct anticoagulant volume:
|anticoagulant volume = (100 – hematocrit)/(595 – hematocrit) x volume of specimen|
b. The tubes must fill completely. A clean venipuncture is essential to avoid activation of
coagulation by tissue thromboplastin.
c. Mix gently by inverting the tube end over end 5–6 times. Avoid vigorous mixing or additional
inversion. Observe for the presence of clots.
- The specimen must be double-centrifuged to prepare a platelet-free plasma specimen (platelet
a. Immediately centrifuge specimen at 1,500 x G for 15 minutes.
b. Carefully remove plasma from cells, avoiding the platelet/buffy coat.
c. Dispense into a plastic tube using a plastic transfer pipette. Do not pour off!
d. Centrifuge the plasma in the plastic tube at 1,500 x G for 15 minutes.
e. Remove the top portion of plasma leaving approximately 500 μL in the bottom to discard.
f. The double-centrifuged plasma should be aliquoted (1.0–2.0 mL each) into properly labeled
plastic tubes. The number of tests ordered will determine the aliquots needed. Generally, a
1.0 mL aliquot per test is required although test volumes may be combined up to 2.0 mL of
plasma per aliquot. Pay particular attention to the amount of specimen required for the ordered
test(s). Coagulation profiles (see individual test specimen requirements) and multiple single-test
orders will require multiple aliquots.
g. After centrifugation, examine the plasma for fibrin clots and pour the cellular portion through
gauze to observe for small red cell clots. Clotted specimens must be discarded and recollected.
- Specimens should be frozen immediately at >-40°C, if possible, and sent in container with at least
5 lbs of dry ice. Specimens must arrive frozen.
- Please include the requested information (see individual test descriptions) as the testing and
interpretations are dependent on clinical history in many of the more complex abnormalities.