Quick Facts
- Sample: Blood (sodium citrate tube)
- Fasting: Not required
- Turnaround Time: 6–8 business days. May take longer based on weather, holiday, or lab delays.
Benefits
- Detect hidden clotting risks before dangerous blood clots form
- Confidential testing without a doctor's order or hospital visit
- Prevent complications like deep vein thrombosis and pulmonary embolism
- Monitor treatment effectiveness if you're on anticoagulant therapy
- Empower proactive care especially if clotting disorders run in your family
Who Is This Test For?
- Individuals with personal or family history of abnormal blood clots
- Young patients who've experienced unexplained thrombosis or clotting events
- Women with recurrent miscarriages possibly linked to clotting abnormalities
- Anyone preparing to start or currently on anticoagulant therapy
- People seeking to understand inherited thrombophilia 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 protein C antigen levels in your blood to detect deficiencies that increase blood clot risk.
Do I need to fast before this test? No, fasting is typically not required unless your provider advises otherwise.
Can medications affect my results? Yes, blood thinners and vitamin K antagonists can alter protein C levels; inform your provider of all medications.
What if my results are abnormal? Low protein C levels warrant consultation with a physician or hematologist for further evaluation and management.
Is this test safe during pregnancy? Yes, it's a standard blood draw; discuss timing and interpretation with your healthcare provider.
More Details
What is the purpose of this test?
The Protein C Antigen Blood Test measures protein C, a vital vitamin K-dependent protein that helps regulate blood clotting. This test identifies inherited or acquired protein C deficiency, which significantly increases your risk of developing abnormal blood clots. Protein C deficiency affects approximately 0.2–0.5% of the general population but appears in 3–5% of patients with venous thromboembolism (Journal of Thrombosis and Haemostasis 2023). By quantifying protein C antigen levels using enzyme-linked immunoassay (ELISA), this test provides critical information for diagnosing clotting disorders, monitoring anticoagulant treatment effectiveness, and evaluating conditions like liver dysfunction or recurrent pregnancy loss.
Who would benefit from this test?
You may benefit from protein C antigen testing if you have a personal or family history of abnormal clotting, especially deep vein thrombosis or pulmonary embolism. Young individuals who've experienced unexplained blood clots should consider this test, as early-onset thrombosis often signals inherited clotting disorders. Women with recurrent miscarriages may have underlying protein C deficiency contributing to pregnancy complications. If you're preparing to start anticoagulant therapy or need ongoing monitoring of treatment effectiveness, this test provides essential baseline and follow-up data. Additionally, anyone with liver disease should consider testing, since protein C is synthesized in the liver and levels reflect hepatic function.
When should I order a Protein C Antigen Blood Test?
Order this test when unexplained blood clots occur, particularly in unusual locations or at a young age. Consider testing before starting anticoagulant therapy to establish baseline protein C levels and guide treatment decisions. If you have a family history of thrombosis or known clotting disorders, proactive screening helps assess your inherited risk. Women experiencing recurrent miscarriages should discuss testing with their healthcare provider, as protein C deficiency may contribute to pregnancy loss. For those already diagnosed with protein C deficiency, periodic monitoring ensures treatment effectiveness and helps adjust anticoagulation strategies. According to clinical guidelines from the American Heart Association, early detection and management of protein C deficiency can reduce venous thrombosis recurrence by up to 50% (AHA 2023).
How do I interpret the results?
- 70–140% – Normal range; no immediate action needed
- 50–70% – Mild deficiency; clinical correlation and monitoring for symptoms recommended
- 25–50% – Moderate deficiency; hematology consultation and possible prophylaxis advised
- Below 25% – Severe deficiency; urgent evaluation and anticoagulation often required
Protein C levels in healthy infants are naturally lower (around 40 IU/dL) compared to adults (65–135 IU/dL), so age-adjusted interpretation is essential.
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 your healthcare provider or lab about all medications you're taking, especially blood thinners or vitamin K antagonists, as these can affect protein C levels. While fasting is typically not required, follow any specific instructions provided by your testing facility. Avoid testing during acute clotting episodes or active thrombosis when possible, as protein C levels may be temporarily altered. If you're on anticoagulant therapy, discuss optimal timing for testing with your provider—some medications require adjustment or temporary discontinuation for accurate results. Blood will be collected via standard venipuncture into a sodium citrate (blue-top) tube. The sample must be processed quickly and plasma separated, then shipped refrigerated for ELISA testing to ensure accurate results.
How often should I get tested?
- Initial screening with family history – Once, then as clinically indicated
- Monitoring anticoagulant therapy – Every 3–6 months or per provider guidance
- After acute thrombotic event – Retest 2–4 weeks after resolution
- Known deficiency, stable condition – Annually or when symptoms change
- Pregnancy planning with history – Before conception and as advised
Testing frequency depends on your individual risk profile and clinical circumstances. If you've been diagnosed with protein C deficiency and are on anticoagulation therapy, regular monitoring helps ensure treatment effectiveness and guides dosage adjustments. For individuals with family history but no personal clotting events, a single baseline test may suffice unless symptoms develop. Always follow your healthcare provider's recommendations for repeat testing based on your specific situation.
Why early detection matters
Early identification of protein C deficiency allows you to take proactive steps to prevent dangerous blood clots before they occur. Deep vein thrombosis and pulmonary embolism are serious, potentially life-threatening complications that can be avoided through appropriate monitoring and preventive anticoagulation when needed. For women with protein C deficiency, early detection helps manage pregnancy-related risks and may improve outcomes in cases of recurrent miscarriage. Knowing your protein C status enables informed decisions about high-risk situations like surgery, long-distance travel, or prolonged immobility—times when clot risk increases. Early detection and proper management reduce the likelihood of thrombosis recurrence, minimize hospitalizations, and lower overall healthcare costs. Simple lifestyle modifications—maintaining healthy weight, avoiding smoking, staying active, and proper hydration—complement medical management and help reduce your clotting risk.
Related tests you may consider
Protein C Functional Blood Test — Measures the functional activity of protein C rather than just antigen levels, providing complementary diagnostic information about how well your protein C actually works.
Protein S Antigen Blood Test — Evaluates another natural anticoagulant whose deficiency often coexists with protein C deficiency, supporting comprehensive thrombophilia evaluation.
Factor V Leiden Mutation Analysis Blood Test — Genetic test for the most common inherited thrombophilia, which can compound clotting risk when present alongside protein C deficiency.
