Test guide
Prothrombin Time Test and INR (PT/INR)
A prothrombin time (PT) test measures how many seconds it takes for a clot to form in a blood sample. Since the results of this test can vary with different labs or test methods, your results may be used to create an INR (international normalized ratio). Using this ratio makes it easier for health care providers to compare and better understand results from different labs or test methods.
What it is for
A PT/INR test is most often used to: A PT/INR test is often done along with a partial thromboplastin time (PTT) test . A PTT test also checks for clotting problems but looks at different coagulation factors than the PT test. Source: MedlinePlus, National Library of Medicine. Medical test information is public domain. Source identity and definition checked automatically on 2026-10-18. No individual clinical interpretation or human reviewer is asserted.
Limitations
Reference intervals and interpretation depend on the laboratory, specimen, method and clinical context. This source definition is educational information; it does not establish a diagnosis, product approval or suitability for an individual.
Also known as
- prothrombin time/international normalized ratio, PT, pro time
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