Prothrombin Time (PT)
Disclaimer: Information on this page is for educational purposes. Consult a physician to interpret your test results. Lissa Health helps track biomarker trends but does not replace medical advice.
What This Test Measures
PT measures the extrinsic coagulation pathway. INR is used for warfarin monitoring.
Prolonged PT occurs with vitamin K deficiency, liver disease, warfarin, and DIC.
Normal Ranges
| Group | Reference Range |
|---|---|
| Men | 11–15 sec (INR 0.8–1.2) |
| Women | 11–15 sec |
| Children | 11–14 sec |
Reference ranges may vary by laboratory and assay method.
Causes of High Levels
- Rarely shortened
Causes of Low Levels
- Warfarin therapy
- Vitamin K deficiency
- Liver disease
- DIC
Test Preparation
- Report warfarin and last dose time
- Stable vitamin K intake
Related Biomarkers
| Biomarker | Relationship |
|---|---|
| Fibrinogen | Clot component |
| D-Dimer | Fibrinolysis |
| Platelets | Primary hemostasis |
FAQ
How often should I take this test?
On warfarin — weekly then monthly when stable.
What should I do if my result is abnormal?
INR >4 or bleeding — urgent contact; subtherapeutic — thrombosis risk.
Last updated: June 2026