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HelpTest Code PCAG Protein C Antigen, Plasma
Ordering Guidance
Coagulation testing is highly complex, often requiring the performance of multiple assays and correlation with clinical information. For that reason, consider ordering AATHR / Thrombophilia Profile, Plasma and Whole Blood.
Testing 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 (warfarin), this should be noted as Coumadin will lower protein C.
Specimen Required
Specimen Type: Platelet-poor plasma
Patient Preparation: Fasting preferred
Collection Container/Tube: Light-blue top (3.2% sodium citrate)
Submission Container/Tube: Plastic vial (polypropylene preferred)
Specimen Volume: 1 mL
Specimen Stability Information: Frozen 2 years
Collection Instructions:
1. For complete instructions, see Coagulation Guidelines for Specimen Handling and Processing.
2. Centrifuge, transfer all plasma into a plastic vial, and centrifuge plasma again.
3. Aliquot plasma into a plastic vial leaving 0.25 mL in the bottom of centrifuged vial.
4. Freeze plasma immediately (no longer than 4 hours after collection) at -20° C or ideally, at or below -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.
Forms
If not ordering electronically, complete, print, and send a Coagulation Test Request (T753) with the specimen.
Useful 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)
This test is not useful for predicting a thrombotic event.
Special Instructions
Method Name
Enzyme-Linked Immunosorbent Assay (ELISA)
Reporting Name
Protein C Ag, PSpecimen Type
Plasma Na CitSpecimen Minimum Volume
0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Plasma Na Cit | Frozen | ||
Reject Due To
| Gross hemolysis | Reject |
| Gross lipemia | Reject |
Clinical Information
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 type 1 (PAI-1).
Expression of the anticoagulant activity of APC is enhanced by a cofactor, protein S, another vitamin K-dependent plasma protein.
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 the patient 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 (warfarin) compounds
-Liver disease
-Intravascular coagulation and fibrinolysis/disseminated intravascular coagulation
Reference Values
Adults: 72%-160%
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.
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.
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 |