What is the Protein C test?

The Protein C blood test measures the level or activity of protein C, a vitamin K–dependent anticoagulant produced by the liver. Protein C plays a critical role in regulating blood clot formation by inactivating clotting factors V and VIII.

When protein C levels are low or its activity is reduced, the balance between clotting and anticoagulation shifts toward thrombosis. Deficiency may be inherited or acquired and can increase the risk of deep vein thrombosis (DVT) and pulmonary embolism.

This test is commonly used as part of a thrombophilia (clotting disorder) assessment.

Why do I need a test for Protein C?

Protein C testing helps identify individuals at increased risk of abnormal blood clotting. Many people with protein C deficiency are unaware until a clot occurs, making proactive testing valuable in high-risk situations.

It is particularly useful in those with unexplained clots, strong family history of thrombosis, or before situations that increase clot risk.

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

• Unprovoked deep vein thrombosis or pulmonary embolism

• Recurrent blood clots

• Family history of clotting disorders

• Clotting at a young age

• Pregnancy complications related to thrombosis

• Long-term anticoagulation consideration

• Pre-travel or pre-surgery clot risk assessment

• Suspected inherited thrombophilia

Benefits of the Protein C test

1. Identifies inherited clotting risk
   Detects protein C deficiency linked to thrombophilia.

2. Supports investigation of unexplained clots
   Useful when standard causes are excluded.

3. Guides preventive strategies
   Helps inform clot risk management decisions.

4. Relevant for family screening
   Inherited deficiency may affect close relatives.

5. Supports pregnancy risk assessment
   Important in clot-related pregnancy complications.

6. Complements other clotting tests
   Often tested alongside Protein S and antithrombin.

7. Non-invasive thrombophilia assessment
   Requires only a blood sample.

8. Improves long-term risk awareness
   Supports informed lifestyle and medical planning.

Step-by-step – how we offer Protein C 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 Protein C results explained

Low Protein C levels or activity

Low levels or reduced activity suggest protein C deficiency, which may be inherited or acquired (e.g., liver disease, vitamin K deficiency, or anticoagulant therapy). This is associated with increased clotting risk.

Clinical context and additional testing are important for confirmation.

UK reference interpretation:

• Low: Below laboratory reference range

Normal Protein C levels

Normal levels indicate adequate natural anticoagulant activity and balanced clot regulation. This suggests no detectable protein C–related clotting disorder.

Results should be interpreted alongside clinical history.

UK reference interpretation:

• Normal: Within laboratory reference range

Borderline or variable results

Borderline results may occur due to temporary factors such as acute illness or medication. Repeat testing may be advised for accurate assessment.

UK reference interpretation:

• Borderline: Near reference limits