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HelpTest ID: PCAG Protein C Antigen, Plasma
Reporting Name
Protein C Ag, PUseful For
Differentiating congenital type I protein C deficiency from type II deficiency
Evaluating the significance of decreased functional protein C, especially when decreased protein C activity might be congenital rather than acquired (eg, due to oral anticoagulant effect, vitamin K deficiency, liver disease, or intravascular coagulation and fibrinolysis/disseminated intravascular coagulation)
Specimen Type
Plasma Na CitAdvisory Information
Coagulation testing is highly complex, often requiring the performance of multiple assays and correlation with clinical information. For that reason, we suggest ordering AATHR / Thrombophilia Profile.
Assay of protein C functional activity (CFX / Protein C Activity, Plasma) is recommended for initial laboratory evaluation of patients suspected of having congenital protein C deficiency (personal or family history of thrombotic diathesis).
Necessary Information
If the patient is being treated with Coumadin, this should be noted as Coumadin will lower protein C.
Specimen Required
See Coagulation Guidelines for Specimen Handling and Processing in Special Instructions.
Patient Preparation: Fasting preferred
Collection Container/Tube: Light-blue top (citrate)
Submission Container/Tube: Plastic vial
Specimen Volume: 1 mL
Collection Instructions:
1. Centrifuge, remove plasma, and centrifuge plasma again.
2. Freeze plasma immediately (no longer than 4 hours after collection) at -20° C or, ideally, ≤-40° C.
Additional Information:
1. Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.
2. Each coagulation assay requested should have its own vial.
Specimen Minimum Volume
0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Plasma Na Cit | Frozen | 14 days |
Special Instructions
Reference Values
Adults: 70%-150%
Normal, full-term newborn infants or healthy premature infants may have decreased levels of protein C antigen (15%-50%), which may not reach adult levels until later in childhood or early adolescence.*
*See Pediatric Hemostasis References section in Coagulation Guidelines for Specimen Handling and Processing in Special Instructions.
Day(s) and Time(s) Performed
Monday through Friday; a.m.
Test Classification
This test has been cleared, approved or is exempt by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.CPT Code Information
85302
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| PCAG | Protein C Ag, P | 27820-0 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 9127 | Protein C Ag, P | 27820-0 |
Clinical Information
Physiology:
Protein C is a vitamin K-dependent anticoagulant proenzyme. It is synthesized in the liver and circulates in the plasma. The biological half-life of plasma protein C is approximately 6 to 10 hours, similar to the relatively short half-life of coagulation factor VII.
Protein C is activated by thrombin, in the presence of an endothelial cell cofactor (thrombomodulin), to form the active enzyme, activated protein C (APC). APC functions as an anticoagulant by proteolytically inactivating the activated forms of coagulation factors V and VIII (factors Va and VIIIa). APC also enhances fibrinolysis by inactivating plasminogen activator inhibitor (PAI-1).
Expression of the anticoagulant activity of APC is enhanced by a cofactor, protein S, another vitamin K-dependent plasma protein.
Pathophysiology:
Congenital homozygous protein C deficiency results in a severe thrombotic diathesis, evident in the neonatal period and resembling purpura fulminans.
Congenital heterozygous protein C deficiency may predispose to thrombotic events, primarily venous thromboembolism. Arterial thrombosis (stroke, myocardial infarction, etc) may occur. Some individuals with hereditary heterozygous protein C deficiency may have no personal or family history of thrombosis and may or may not be at increased risk.
The 2 types of hereditary heterozygous protein C deficiencies that are recognized are:
-Type I (concordantly decreased protein C function and antigen)
-Type II (decreased protein C function with normal antigen)
Acquired deficiency of protein C may occur in association with:
-Vitamin K deficiency
-Oral anticoagulation with Coumadin compounds
-Liver disease
-Intravascular coagulation and fibrinolysis/disseminated intravascular coagulation (ICF/DIC)
Interpretation
Values less than 70% to 75% may represent a congenital deficiency state, if acquired deficiencies can be excluded.
Protein C antigen and activities generally are undetectable in individuals with severe, homozygous protein C deficiency.
Acquired protein C deficiency is of uncertain clinical hemostatic significance.
The clinical significance of increased protein C is unknown.
Clinical Reference
1. Mannucci PM, Owen WG: Basic and clinical aspects of proteins C and S. In Haemostasis and Thrombosis. Second edition. Edited by AL Bloom, DP Thomas. Edinburgh, Churchill Livingstone, 1987, pp 452-464
2. Marlar RA, Mastovich S: Hereditary protein C deficiency: a review of the genetics, clinical presentation, diagnosis and treatment. Blood Coagul Fibrinolysis 1990;1:319-330
3. Marlar RA, Montgomery RR, Broekmans AW: Diagnosis and treatment of homozygous protein C deficiency. Report of the Working Party on Homozygous Protein C Deficiency of the Subcommittee on Protein C and Protein S, International Committee on Thrombosis and Haemeostasis. J Pediatr 1989;114:528-534
4. Miletrich J, Sherman L, Broze G Jr: Absence of thrombosis in subjects with heterozygous protein C deficiency. N Engl J Med 1987;317:991-996
5. Pabinger I, Allaart CF, Hermans J, et al: Hereditary protein C-deficiency: laboratory values in transmitters and guidelines for the diagnostic procedure. Report on a study of the SSC Subcommittee on Protein C and Protein S. Protein C Transmitter Study Group. Thromb Haemost 1992;68:470-474
Analytic Time
3 daysMethod Name
Enzyme-Linked Immunosorbent Assay (ELISA)
Forms
If not ordering electronically, complete, print, and send a Coagulation Test Request (T753) with the specimen.
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