Protein C and Protein S Test

Overview

The Protein C and Protein S Test evaluates two important natural anticoagulants in the blood that help regulate clot formation. Protein C is a vitamin K–dependent glycoprotein synthesized in the liver. It circulates as an inactive zymogen and, when activated by the thrombin–thrombomodulin complex, becomes Activated Protein C (APC), a serine protease that prevents excessive coagulation.

Protein S is also a vitamin K–dependent glycoprotein synthesized by hepatocytes, endothelial cells, and megakaryocytes. It exists in two forms: free (active) and bound (inactive). Free Protein S functions both independently and as a cofactor for Activated Protein C, helping to inactivate clotting factors Va and VIIIa. Together, Protein C and Protein S maintain hemostatic balance and prevent excessive clot formation.

Deficiencies in Protein C or S, whether inherited or acquired, lead to a hypercoagulable state and increase the risk of venous thromboembolism (VTE), including deep vein thrombosis (DVT) and pulmonary embolism (PE).

Symptoms

Abnormal Protein C and Protein S levels do not produce direct symptoms but manifest as complications related to abnormal clotting:

1. Deep Vein Thrombosis (DVT): Pain, swelling, redness, or warmth in the legs.
2. Pulmonary Embolism (PE): Sudden shortness of breath, chest pain, rapid heart rate, or coughing up blood.
3. Warfarin-Induced Skin Necrosis: Painful skin lesions and necrosis shortly after starting warfarin, more common in Protein C deficiency.
4. Neonatal Purpura Fulminans: Severe, life-threatening clotting disorder in newborns with congenital Protein C deficiency, leading to skin necrosis and disseminated intravascular coagulation (DIC).
5. Recurrent Miscarriages or Pregnancy Complications: Linked to Protein S deficiency.

Causes

Deficiencies in Protein C and Protein S may be hereditary or acquired:

1. Hereditary Deficiency:
   1. Protein C deficiency occurs in about 1 in 300 individuals.
   2. Protein S deficiency is rarer, found in about 1 in 20,000.
   3. Both are inherited in an autosomal dominant pattern.
2. Acquired Deficiency:
   1. Liver Disease: Impaired synthesis due to liver failure.
   2. Vitamin K Deficiency: Since both proteins are vitamin K-dependent.
   3. Warfarin Therapy: Reduces Protein C and Protein S activity.
   4. Pregnancy and Oral Contraceptive Use: Naturally lower Protein S activity.
   5. Sepsis and DIC: Rapid consumption of clotting factors reduces levels.
   6. Acute Medical Conditions: Stroke, myocardial infarction, pancreatitis, and systemic inflammatory disorders.

Risk Factors

Individuals more likely to have Protein C and Protein S abnormalities include:

1. Family History of Thrombosis: Genetic mutations leading to inherited deficiencies.
2. Patients with Previous VTE: Recurrent DVT or PE suggests underlying Protein C or S deficiency.
3. Pregnant Women: Physiological reduction in Protein S increases clotting risk.
4. Individuals on Warfarin Therapy: Increased risk of skin necrosis without proper heparin bridging.
5. Patients with Chronic Liver Disease: Reduced synthesis of vitamin K–dependent clotting proteins.
6. People with Inflammatory or Autoimmune Disorders: May experience acquired deficiencies.
7. Children or Neonates with Severe Deficiency: At risk of neonatal purpura fulminans.

Prevention

Preventive strategies focus on minimizing clotting risk in individuals with Protein C or S deficiencies:

1. Diagnostic Testing:
   1. Indicated for patients with unexplained blood clots, family history of thrombosis, pregnancy complications, or during anticoagulant therapy monitoring.
   2. Assay methods include clot-based assays, chromogenic assays, and ELISA.
2. Sample Collection:
   1. Collect about 5 mL of blood in sodium citrate tubes (blue-capped).
   2. Plasma should be separated quickly and transported to the lab within 4 hours at ambient temperature, or frozen at -20°C if delayed.
3. Precautions Before Testing:
   1. Stop anticoagulants such as warfarin at least two weeks before testing.
   2. Stay hydrated and avoid physical or emotional stress 24 hours before collection.
4. Clinical Management:
   1. Anticoagulation: Heparin, direct oral anticoagulants (DOACs), or cautious use of warfarin with bridging therapy.
   2. Protein C Concentrate or Fresh Frozen Plasma: Used in severe neonatal deficiency or purpura fulminans.
   3. Monitoring in Pregnancy: High-risk women may require close surveillance and prophylactic anticoagulation.
5. Lifestyle Measures:
   1. Maintaining a healthy weight, regular exercise, and avoiding smoking help reduce clotting risk.
   2. Genetic counseling for families with inherited deficiencies.