Definition

The PT test measures how many seconds it takes for a clot to form in a blood sample. The INR is a standardized ratio that makes this result comparable between different laboratories.

Purpose

Monitors the effectiveness and dosing of warfarin (blood thinner) therapy. Investigates signs of unusual bleeding or clotting. Assesses clotting ability before surgery. Screens for liver disease or vitamin K deficiency.

Results

  • Low INR, the blood is clotting too quickly, increased risk of dangerous clots
  • High INR, the blood is clotting too slowly, increased risk of bleeding

Normal Values

Laboratory-specific and indication-specific. The target INR range is set by the physician according to why the patient is taking warfarin.

Risks and Limitations

Factors that affect the results: alcohol consumption, foods rich in vitamin K (green leafy vegetables, soybean/canola oil), a high-fat diet, and medications and supplements taken at the same time.

Related Tests

aPTT (Activated Partial Thromboplastin Time)

Measures the number of seconds it takes for blood to clot. Unlike PT, it evaluates a different subset of clotting factors and their function.

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Liver Function Tests (AST, ALT, ALP, GGT)

A group of tests that evaluate liver health. Main components

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D-Dimer

D-dimer is a protein fragment that appears when a clot dissolves in the body. Its level in the blood shows whether clot formation or breakdown is ongoing.

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