What is the Prothrombin Time test?

The Prothrombin Time (PT) blood test measures the time it takes for blood to clot via the extrinsic and common coagulation pathways. It assesses the function of several clotting factors, including factors I, II, V, VII, and X.

PT is widely used to evaluate bleeding or clotting disorders, monitor anticoagulant therapy (such as warfarin), and assess liver function, as many clotting factors are produced by the liver.

Results are often reported as PT seconds and/or International Normalised Ratio (INR).

Why do I need a test for Prothrombin Time?

Prothrombin Time testing helps identify abnormalities in blood clotting that may increase the risk of bleeding or thrombosis. It is also an important tool in monitoring anticoagulant therapy and assessing liver-related clotting impairment.

This test is commonly requested before surgery, during anticoagulant treatment, or when unexplained bleeding or bruising occurs.

You may benefit from this test if you experience or have:

• Easy bruising or unexplained bleeding

• Prolonged bleeding after injury or surgery

• Liver disease or suspected liver dysfunction

• Use of anticoagulant medication

• Pre-operative clotting assessment

• Vitamin K deficiency concerns

• Monitoring of clotting disorders

• Unexplained abnormal coagulation results

Benefits of the Prothrombin Time test

1. Assesses blood clotting efficiency
   Measures how quickly blood forms a clot.

2. Supports anticoagulant therapy monitoring
   Essential for managing warfarin treatment.

3. Evaluates liver function impact on clotting
   Clotting factors depend on liver synthesis.

4. Identifies bleeding risk
   Helps detect delayed clotting tendencies.

5. Useful in pre-surgical screening
   Ensures safe clotting before procedures.

6. Detects vitamin K–related clotting issues
   PT is sensitive to vitamin K deficiency.

7. Supports diagnosis of coagulation disorders
   Useful in inherited or acquired conditions.

8. Non-invasive coagulation assessment
   Requires only a blood sample.

Step-by-step – how we offer Prothrombin Time testing

Clinic-based testing (UK-wide)

• Choose your nearest UK clinic

• Attend your appointment

• Blood sample collected by a qualified clinician or phlebotomist

• Sample is sent to the laboratory for analysis

At-home or hotel testing (+£60)

• A qualified phlebotomist visits your home or hotel

• Blood sample collected in a comfortable, familiar setting

• No clinic visit or travel required

Both services are available UK-wide.

Your Prothrombin Time results explained

Shortened or low PT / INR

A shorter-than-normal PT is uncommon and usually not clinically significant. It may reflect increased clotting tendency in rare situations.

Interpretation depends on clinical context.

UK reference interpretation:

• Low: Below laboratory reference range

Normal Prothrombin Time

Normal PT and INR indicate balanced clotting factor activity and effective coagulation. This suggests no significant clotting or bleeding disorder at the time of testing.

UK reference interpretation:

• Normal PT: ~11–13.5 seconds

• Normal INR: 0.8–1.2

Prolonged PT / high INR

A prolonged PT or elevated INR indicates delayed blood clotting. Causes include liver disease, vitamin K deficiency, anticoagulant therapy, or clotting factor deficiency.

This may increase bleeding risk and requires clinical correlation.

UK reference interpretation:

• Prolonged PT: >13.5 seconds

• High INR: >1.2 (non-anticoagulated individuals)