Prothrombin Time, Plasma
Use
Prothrombin time (PT) is used as a screening test to detect a deficiency of one or more of the clotting factors of the extrinsic coagulation system (I, II, V, VII, or X) due to a hereditary or acquired deficiency, liver disease, vitamin K deficiency, or presence of inhibitors. It is also used in monitoring the intensity of oral anticoagulant therapy when combined with international normalized ratio (INR) reporting. PT may be prolonged due to deficiencies of clotting factors, presence of inhibitors, or oral anticoagulation therapy.
Special Instructions
Proper specimen collection and handling are critical. For accurate results, a double-centrifuged specimen is necessary to avoid platelet contamination. The test requires prompt freezing of the plasma if not tested immediately. Refer to Mayo's Coagulation Guidelines for additional specimen handling instructions.
Limitations
PT is not useful for detecting deficiencies of coagulation factors that do not influence the prothrombin time test, such as factors VIII, IX, XI, XII, XIII. The activity of coagulation factor V can be lower in frozen-thawed plasma, leading to falsely prolonged PT. PT may also be prolonged in patients receiving heparin, particularly at higher concentrations.
New York Approved
Methodology
Automated Analyzer (Coagulation)
Biomarkers
LOINC Codes
- 34528-0
- 5902-2
- 6301-6
Result Turnaround Time
1 day
Related Documents
For more information, please review the documents below
Specimen
Plasma
Volume
1 mL
Minimum Volume
0.5 mL
Container
Plastic vial
Collection Instructions
Centrifuge, remove plasma, and centrifuge again. Aliquot plasma into a plastic vial leaving 0.25 mL in the bottom. Follow Coagulation Guidelines.
Causes for Rejection
Gross hemolysis
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 24 hours |
| Frozen | 30 days |