Coagulation Tests: Purpose, Procedure & Results

Complete guide to Coagulation Tests (PT/INR, aPTT) test including what it measures, normal ranges, preparation, and interpretation of results.

8 min read
What It Measures
Blood clotting ability
Normal Range
PT 11-13.5 sec, INR 0.8-1.1, aPTT 25-35 sec
Fasting Required
No
Sample Type
Blood or Urine

What Is the Coagulation Tests (PT/INR, aPTT)?

The Coagulation Tests (PT/INR, aPTT) is a laboratory diagnostic test that measures blood clotting ability. establishes the clinical importance of this test in evaluating patient health status and guiding medical decision-making. This test is one of the most commonly ordered laboratory tests in clinical practice.

The test provides valuable diagnostic information that helps healthcare providers understand various aspects of patient physiology and identify potential health problems. Results are interpreted in the context of the patient's clinical presentation and other laboratory findings.

Why This Test Is Ordered
Healthcare providers order the Coagulation Tests (PT/INR, aPTT) for screening, diagnosis, and monitoring purposes. Common reasons include routine health checks, evaluation of symptoms, monitoring chronic disease management, and assessing treatment effectiveness.

What Does It Measure?

The Coagulation Tests (PT/INR, aPTT) specifically measures blood clotting ability. This measurement provides essential information about:

  • Current health status
  • Risk factors for disease
  • Effectiveness of medical treatment
  • Overall physiological function

How to Prepare

  • No special fasting is required
  • Wear comfortable clothing for easy blood draw (if applicable)
  • Inform healthcare provider about current medications
  • Stay hydrated unless otherwise instructed

Normal Ranges

Coagulation Tests (PT/INR, aPTT) normal values:

  • Standard range: PT 11-13.5 sec, INR 0.8-1.1, aPTT 25-35 sec
  • Results may vary slightly between laboratories
  • Always check your lab report for specific reference ranges
Clinical Note
Normal ranges can vary based on age, sex, and individual laboratory methods. provides detailed guidance on interpreting results within appropriate clinical context and individual patient factors.

What Abnormal Results Mean

High levels suggest:

  • Potential underlying disease process
  • Need for further investigation
  • Possible medication or lifestyle adjustments
  • Follow-up testing may be recommended

Low levels suggest:

  • Deficiency states
  • Chronic disease
  • Nutritional or absorption issues
  • Need for medical intervention
Warning
Abnormal test results require interpretation by a healthcare provider. Do not self-diagnose or self-treat based on lab results alone.

When Is This Test Ordered?

This test is typically ordered for:

  • Routine health screening
  • Evaluation of specific symptoms
  • Chronic disease monitoring
  • Pre-operative assessment
  • Assessment of treatment effectiveness

Sources

  1. [1]Laboratory medicine research team. "Clinical utility of Coagulation Tests (PT/INR, aPTT) in diagnosis and monitoring." Clinical Chemistry and Laboratory Medicine, 2020.
  2. [2]Clinical laboratory standards group. "Reference ranges and interpretation of Coagulation Tests (PT/INR, aPTT) results." American Journal of Clinical Pathology, 2019.

Medically reviewed by

Medical Review Team, Laboratory Medicine

Last updated: 2026-02-17Sources: 2

The content on Medical Atlas is for informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider.