Skip to contentSkip to navigation
COVID-19: We are open. Some services are modified. Mask is mandatory. Details at

Prothrombin Time and International Normalized Ratio


PT INR (prothrombin time) is mainly used to monitor patients under chronic treatment with warfarin (Coumadin®), an agent that prevents the formation of blood clots in at-risk individuals (atrial fibrillation, artificial heart valves, deep vein thrombosis [phlebitis], pulmonary embolism, coagulation abnormalities such as antiphospholipid syndrome, occasionally after a myocardial infarction). PT INR is used to adjust the dose of warfarin to achieve a balance between clotting risk and excessive bleeding.

A PT INR greater than 4.5 is problematic and should be reported to the attending physician without delay. Other results should be interpreted based on treatment targets, which differ from one clinical condition to another. Diseases and some medications may alter PT INR. Alcohol and certain vitamin K-rich foods such as beef or pork liver, green tea, broccoli, chickpeas, kale, turnip fans and soybeans can change the result. Difficulties at the time of collection may also interfere.

Term of the Week

Hot zone

A hot zone is a section of a facility (sometimes an entire facility or even a city district) where there is a high risk of contamination by patients with an infectious disease. All individuals entering a hot zone must respect appropriate protective measures. By analogy, “cold zone” and “warm zone” are used to refer to areas where there is no infected individual or only individuals suspected of having an infection.