Prothrombin Time

Specimen Type: Whole blood
Collection Container: Light-blue top (3.2% sodium citrate)
Specimen Volume: 3 mL

Specimen Type: Platelet-poor plasma
Collection Container: Light-blue top (3.2% sodium citrate)

1. Collect sample, ensuring tube is completely filled to obtain a 9:1 (blood to anticoagulant) ratio.
2. Submit sealed, unopened sample to laboratory.

1. Draw blood into a light blue (sodium citrate) tube.  Be sure to fill tubes completely.
2. Mix gently 5 to 6 times (do not over mix).
3. Centrifuge the sample for 10 minutes.
4. Using a pipette, aliquot plasma into a plastic vial being careful not disturb the buffy coat.
5. Centrifuge the plasma sample a second time for 10 minutes
6. Using a pipette, aliquot the top portion of plasma into a plastic vial.  Be careful not to disturb the sediment at the bottom (leave approx. 0.25 mL of plasma at the bottom).
7. Label each tube as "Plasma."
8. Immediately freeze samples

Whole Blood
Room temperature: 24 hours
Refrigerated: Unacceptable
Frozen: Unacceptable

Platelet-poor plasma
Room temperature: 24 hours
Refrigerated: Unacceptable
Frozen (-20  °C): 2 weeks
Frozen (-70  °C): 6 months

Daily

Same day / 1 day

1. Many commonly administered drugs affect the results obtained in PT testing. (Example: coumadin, heparin and direct thrombin inhibitors such as hirudin and argatroban).
2. STA^® Neoplastine^® CI and CI+, both contain a specific inhibitor of heparin. Therefore, only levels of heparin outside of the therapeutic range will affect the PT results. The test is insensitive to unfractionated heparin levels up to 1 IU/ml and to low molecular weight heparin levels up to 1.5 anti-Xa IU/ml.
3. The correct blood/anticoagulation sample volume ratio of 9:1 must be respected.
4. Do not keep plasmas at 2-8 ° C because in this temperature range the Factor VII may be activated by the kallikrein system.