Quick Facts
- Sample: Blood (plasma)
- Fasting: Not required
- Turnaround Time: 5–7 business days. May take longer based on weather, holiday, or lab delays.
Benefits
- Early clot-risk detection — Identify protein C deficiency before serious thrombosis occurs
- Direct access — Order online and visit a local lab without a doctor's referral
- Fast, precise results — Chromogenic assay delivers accurate functional activity measurements in days
- Proactive prevention — Understand your clotting profile to guide lifestyle and treatment decisions
- Confidential & secure — Results accessible in online account within days
Who Is This Test For?
- Individuals with unexplained or recurrent blood clots at a young age
- Those with a family history of clotting disorders or thrombosis
- People experiencing clots in unusual locations (e.g., abdomen, brain)
- Patients on anticoagulant therapy requiring monitoring of protein C levels
- Health-conscious consumers seeking preventive insights into cardiovascular risk factors
How It Works – Just 3 Steps
- Order online — Select your test, pay securely, and schedule your blood draw.
- Visit a lab — Get your blood drawn at any of the 2,000+ convenient lab locations nationwide.
- Receive results — Access results online in your secure account within days.
FAQ
What does this test measure? It measures the functional activity of protein C, a natural anticoagulant that prevents excessive clotting.
Can I take this test while on blood thinners? Yes, but warfarin and similar medications can lower protein C levels; inform the lab of all medications.
Do I need to fast before the test? No, fasting is not required for the Protein C Functional Blood Test.
What happens if my results are abnormal? Low protein C activity suggests deficiency or dysfunction; consult a healthcare provider for further evaluation and potential repeat testing.
How is this different from genetic clotting tests? This test measures how well protein C functions, while genetic tests (like Factor V Leiden) identify inherited mutations.
More Details
What is the purpose of this test?
The Protein C Functional Blood Test assesses whether protein C—a vital anticoagulant protein in your blood—is working properly to regulate clot formation. Protein C helps prevent excessive clotting by inactivating clotting factors Va and VIIIa (Mayo Clinic Labs 2016). When protein C activity is too low, your risk of developing dangerous blood clots (venous thromboembolism) increases significantly (UCSF Health 2023).
Who would benefit from this test?
This test is valuable for people investigating unexplained clotting events or assessing inherited clotting risk. Individuals who have experienced deep vein thrombosis (DVT), pulmonary embolism, or clots at a young age (under 50) should consider testing. Those with multiple family members affected by clotting disorders may carry genetic protein C deficiency, which affects approximately 0.2–0.5% of the general population (UCSF Health 2023). Patients already on anticoagulation therapy may also benefit from periodic monitoring.
When should I order a Protein C Functional Blood Test?
Order this test if you've had blood clots without clear cause, such as after surgery or injury. Consider testing if you've experienced recurrent clots, clots in unusual locations (cerebral, mesenteric, or portal veins), or pregnancy-related clotting complications. If multiple relatives have had thrombosis, screening before high-risk situations (surgery, pregnancy, or starting hormone therapy) can inform preventive strategies (MedlinePlus 2021). Testing is most accurate when performed at least 2–4 weeks after an acute clotting event and when not actively clotting.
How do I interpret the results?
Protein C activity is reported as a percentage of normal function or in international units per deciliter (IU/dL). Here's what different ranges typically indicate:
- 70–150% – Normal anticoagulant function; no immediate concern, routine wellness monitoring
- 50–70% – Borderline low activity; repeat testing and evaluate medication effects and clinical context
- 20–50% – Mild to moderate deficiency; consult healthcare provider and consider anticoagulation during high-risk periods
- Below 20% – Severe deficiency; medical evaluation required, increased clot risk may warrant treatment
Early identification of protein C deficiency through functional testing reduces the risk of life-threatening clots and associated healthcare costs substantially (American Heart Association 2022).
Disclaimer: Reference ranges may vary by laboratory. Listed ranges are general guidelines and may differ from those used by the performing lab. Always consult your healthcare provider for interpretation.
Pre-test preparation
Inform the lab about all medications you're taking, especially anticoagulants like warfarin, which can artificially lower protein C levels. Your healthcare provider may advise temporarily pausing certain medications before testing. No fasting is required. Avoid testing during acute illness, active clotting, or pregnancy when possible, as these conditions can temporarily affect protein C levels. Wear comfortable clothing with sleeves that roll up easily for venipuncture.
How often should I get tested?
Testing frequency depends on your clinical situation and risk factors:
- Initial screening for unexplained clots – Once, with possible confirmation test 2–4 weeks later
- Family history but no clotting events – Once for baseline; repeat only if symptoms develop
- On anticoagulation therapy – Every 3–6 months or as directed by healthcare provider
- Before high-risk situations (surgery, pregnancy) – Once, 2–4 weeks before planned event
- After confirmed deficiency diagnosis – Annually or when treatment changes
Why early detection matters
Protein C deficiency significantly increases your risk of venous thromboembolism, which can lead to potentially fatal complications like pulmonary embolism. Early detection allows for preventive strategies during high-risk periods—such as surgery, long flights, pregnancy, or hormone therapy—when clot risk naturally increases. Identifying deficiency before a clotting event enables you and your healthcare provider to implement targeted anticoagulation, lifestyle modifications, and monitoring protocols. Early intervention reduces hospitalizations, prevents chronic complications like post-thrombotic syndrome, and can be lifesaving (American Heart Association 2022).
Related tests you may consider
Protein S Functional Test — Often ordered alongside protein C testing to identify combined deficiencies affecting natural anticoagulation.
Factor V Leiden Mutation Test — Genetic test for the most common inherited clotting disorder; helps differentiate genetic causes.
D-Dimer Test — Detects active clot breakdown products; useful for ruling out acute thrombosis in symptomatic patients.
