PT-INR

Overview

Prothrombin time–International Normalized Ratio (PT‑INR) is a standardized measure of how long blood takes to clot via the extrinsic coagulation pathway. The laboratory reports prothrombin time (PT) adjusted to an INR to allow comparison between labs. It is used to detect bleeding tendency or clotting dysfunction, monitor vitamin K antagonist therapy (e.g., warfarin), and help evaluate liver synthetic function, vitamin K status, and disseminated intravascular coagulation. Indications for testing include unexplained bruising, prolonged bleeding after injury or procedures, hematuria, melena, or monitoring anticoagulant therapy. INR is generally similar across adults but can be higher in newborns, altered in severe liver disease, and influenced by pregnancy, age-related comorbidities, and interacting medications.

Test Preparation

• A duly filled coagulation requisition form (Annexure - CR/05) is mandatory for sample collection
• Overnight fasting is preferred but not mandatory
• Kindly provide complete clinical details and medication history or doctor's prescription
• this information is important for correlation of your test results

Why Do I Need This Test

• Included in coagulation/CBC-related profiles to assess bleeding risk and anticoagulation control.
• Symptoms: unexplained bleeding, excessive bruising, bleeding after surgery, or signs of thrombosis if therapy is inadequate.
• Diagnoses/monitoring: anticoagulant monitoring (warfarin), liver disease, vitamin K deficiency, DIC.
• Abnormal values may reflect anticoagulant effect, impaired clotting factor synthesis, deficiency of vitamin K, or consumptive coagulopathy.
• Lifestyle/medication interactions (alcohol, diet high/low in vitamin K, antibiotics, herbal drugs) can alter INR.
• Family history of bleeding disorders or liver disease may prompt testing.

Understanding Test Results

• INR 0.8–1.2: normal coagulation for an untreated individual.
• INR <0.8 (e.g., <0.5): suggests faster clotting and a possible higher thrombotic risk; may reflect lab variation or excess vitamin K/insufficient anticoagulation.
• INR 1.3–1.9: mildly prolonged; could indicate mild liver dysfunction, vitamin K insufficiency, early anticoagulant effect, or lab variation.
• INR 2.0–3.0: commonly considered therapeutic for many indications (e.g., atrial fibrillation, DVT).
• Values in this range are expected and monitored in patients on warfarin.
• INR 2.5–3.5: target range for some high-risk situations (certain mechanical heart valves); higher bleeding risk as INR rises.
• INR >3.5–5.0: elevated bleeding risk; review medications, diet, and consider dose adjustment or reversal if bleeding.
• INR >5.0 (especially >8.0): high risk of serious bleeding; urgent evaluation and reversal (vitamin K, plasma/prothrombin complex concentrate) may be required.
• Always interpret INR in clinical context (indication for anticoagulation, concurrent drugs, liver function, and symptoms).
• Neonates have physiologically prolonged PT/INR compared with adults.

FAQs