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Activated Partial Thromboplastin Time (aPTT)

Published: July 27, 2026Updated: August 25, 2026

The aPTT measures the time it takes for blood to clot through the intrinsic and common coagulation pathways.

Quick summary

aPTT assesses the intrinsic and common coagulation pathways.

Medically reviewed by WellAlly Editorial TeamLast reviewed August 25, 2026Editorial policy

Key facts at a glance

Units
seconds
Clinical utility
diagnostic
Result kind
quantitative
FDA-cleared
FDA Cleared Coagulation Assay
interpretation: {"text":"May indicate a deficiency in clotting factors (e.g., factor VIII, IX, XI), the presence of inhibitors, or the effect of anticoagulant therapy.","label":"Prolonged aPTT"}; {"text":"May suggest a higher risk of thrombosis or could be a normal variation depending on the clinical context.","label":"Shortened aPTT"}

The activated partial thromboplastin time (aPTT) test is a common coagulation test that evaluates the function of specific clotting factors in the blood. It is particularly useful in diagnosing bleeding disorders and monitoring anticoagulant therapy.

The test measures the time it takes for a clot to form after reagents are added to the blood sample. A prolonged aPTT can indicate a deficiency in clotting factors or the presence of inhibitors.

Normal aPTT values typically range from 25 to 35 seconds. Deviations from this range may require further investigation to identify the underlying cause.

Frequently asked questions

What is the normal range for aPTT?
The normal range for aPTT is typically between 25 and 35 seconds.
What does a prolonged aPTT mean?
A prolonged aPTT may indicate a bleeding disorder, a deficiency in clotting factors, or the presence of inhibitors.
  1. 1
    Activated Partial Thromboplastin Time (aPTT)Source
  2. 2
    Coagulation TestsSource

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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 25, 2026. · Read our editorial policy