Protein C and Protein S



Protein C activity or protein C functional; protein C antigen; Protein S antigen, free.


To assess coagulation function and assist in diagnosis of disorders such as thrombosis related to protein C and protein S deficiency.

Patient Preparation

There are no food, fluid, or activity restrictions unless by medical direction. Patients should discontinue warfarin therapy for 2 wk prior to specimen collection, as ordered. Specimen collection should not be performed sooner than 10 days following a thrombotic or clotting event.

Normal Findings

AgeProtein C Activity or Functional Protein C (Method: Electromagnetic Mechanical Clot Detection)AgeProtein C Antigen (Method: Enzyme Immunoassay)
3–6 mo28%–80%3–6 mo28%–80%
1–6 yr40%–90%1–6 yr40%–90%
7–11 yr68%–140%7–11 yr68%–140%
12–13 yr65%–160%12–13 yr65%–160%
14 yr–Adult70%–170%14 yr–Adult70%–140%
Values are significantly reduced in children because of liver immaturity. Functional Protein C and Free Protein S antigen, free are recommended for initial screening of Protein C and Protein S deficiency. The two are initially tested together because a deficiency in Protein S may affect Protein C activity. Protein C antigen is used to further distinguish inherited type 1 from inherited type 2 protein C deficiency.
AgeProtein S Free Antigen (Method: Microlatex Particle-Mediated Immunoassay)AgeProtein S Activity or Functional Protein S (Method: Electromagnetic Mechanical Clot Detection)AgeProtein S Total Antigen (Method: Enzyme Immunoassay)
Newborn–3 mo15%–55%Newborn–3 mo15%–55%Newborn12%–60%
3–6 mo35%–90%3–6 mo35%–90%1 wk–29 day25%–80%
7–12 mo45%–115%7–12 mo45%–115%1–89 day30%–95%
1–5 yr60%–120%1–5 yr60%–120%3 mo–5 yr55%–120%
6–9 yr60%–130%6–13 yr60%–150%6–10 yr40%–115%
10–17 yr60%–140%14–17 yr50%–145%11 yr–Adult male85%–135%
18 yr–Adult male75%–145%18 yr–Adult male70%–140%11 yr–Adult female65%–130%
18 yr–Adult male55%–125%18 yr–Adult female60%–130%
Values are significantly reduced in children because of liver immaturity; levels reach normal adult levels within 3 to 6 months of age. Protein S Free Antigen or Functional Protein S may be used to identify Protein S deficiency. Protein S Total Antigen is used to further distinguish inherited types I, II, or III Protein S deficiency.

Critical Findings and Potential Interventions


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