protein C, protein S
المؤلف:
Kathleen Deska Pagana, Timothy J. Pagana, Theresa Noel Pagana.
المصدر:
Mosbys diagnostic and laboratory test reference
الجزء والصفحة:
15th edition , p746-747
2025-08-14
486
Type of test Blood
Normal findings
Protein S: 60%-130% of normal activity
Protein C: 70%-150% of normal activity
Protein C levels are lower in females and decrease with age in both males and females.
Test explanation and related physiology
The plasma coagulation system is tightly regulated between thrombosis and fibrinolysis. This precise regulation is important. The protein C–protein S system is an important regulator of coagulation. Protein C inhibits the regulation of activated factor VIII and factor V see Figure C3. This function of protein C is enhanced by protein S. Congenital deficiencies of these vitamin K–dependent proteins may cause spontaneous intravascular thrombosis. Furthermore, dysfunctional forms of the proteins result in a hypercoagulable state. In addition, nearly 50% of hypercoagulable states are caused by the presence of a factor V (factor V Leiden) that is resistant to protein C inhibition. Acquired deficiencies are less commonly symptomatic.
These proteins are vitamin K dependent and are decreased in patients who are taking warfarin (Coumadin), in liver dis eases, and in severe malnutrition. These are some of the causes of acquired decreased protein S and C activity. Because complement regulatory proteins are acute phase reactants, autoimmune diseases and other inflammatory diseases are associated with increased binding of protein S causing an acquired protein S deficiency. Affected patients may experience hypercoagulable events. Measurement of plasma-free protein S antigen is performed as the initial testing for protein S deficiency.
When decreased activity of these proteins is identified, more testing is required. For example, congenital protein C deficiency is classified into two types. Type I deficiency is characterized by decreased protein synthesis or increased intracellular protein degradation that leads to lower levels of protein C in blood. Type I deficiency accounts for about 75% of all cases of congenital protein C deficiency. Type II deficiency is characterized by dysfunctional protein C that is produced in normal amounts. Protein C antigen testing (PCAG / Protein C Antigen) is helpful to distinguish between type I and type II deficiencies. If decreased protein antigen is found, Protein C (PROC) gene encodes for protein C and can be evaluated by DNA sequencing.
Interfering factors
• Decreased protein C may occur in the postoperative state.
• Pregnancy or the use of exogenous sex hormones is associated with decreases in proteins C and S.
• Active clotting states, such as vein thrombosis, can lower levels of proteins S and C. Drugs that can decrease levels include vitamin K inhibitors (e.g., Coumadin). Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no • Blood tube commonly used: blue
• If more than one blood test is to be obtained, draw the blood for protein C or S second to avoid contamination with tissue thromboplastin that may occur in the first tube. If only blood for protein C or S is being drawn, draw a red-top tube first (and throw it away), and then draw the blood for this study in a blue-top tube (two-tube method of blood draw).
* If the patient is found to be deficient in either protein, encourage the patient’s family members to be tested, because they may be similarly affected.
Abnormal findings
Decreased levels
- Congenital deficiency of protein C or protein S
- DIC
- Hypercoagulable states
- Pulmonary emboli
- Arterial or venous thrombosis
- Vitamin K deficiency because of drugs or malnutrition
- Malignancy
- Autoimmune diseases
- Inflammation
- Warfarin
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