From the Research
Protein C deficiency is typically diagnosed when the percentage activity of protein C is below 60-70% of normal, as stated in the most recent study 1. Specifically:
- Mild deficiency: 20-60% activity
- Moderate deficiency: 1-20% activity
- Severe deficiency: <1% activity To diagnose, doctors will order a protein C activity blood test. Results below 60-70% on two separate occasions, at least 4-6 weeks apart, are generally considered diagnostic. Family history and clinical symptoms are also taken into account. It's essential to consider that protein C levels can be temporarily lowered by certain conditions like liver disease, vitamin K deficiency, or use of vitamin K antagonists (e.g. warfarin), as noted in 2 and 3. Therefore, testing should be done when the patient is not acutely ill or on anticoagulation therapy for accurate results. Protein C is a crucial natural anticoagulant, and deficiency increases the risk of abnormal blood clotting, particularly deep vein thrombosis and pulmonary embolism, as highlighted in 4 and 5. Understanding the degree of deficiency helps guide treatment decisions, which may include anticoagulation therapy in some cases. Key points to consider in diagnosis and management include:
- The importance of using a clotting time-based or chromogenic activity assay as the initial test for protein C deficiency, as recommended in 3
- The need to exclude acquired causes of protein C deficiency, such as liver disease or vitamin K deficiency, as discussed in 2 and 1
- The potential for falsely normal results due to lupus anticoagulants or direct thrombin inhibitors, as noted in 3