Protein C, Functional

Also known as: Functional Protein C, Protein C Activity (Chromogenic)

Clinical Use

Order Test

Use

Confirmation and characterization of protein C deficiency

Special Instructions

Not provided.

Limitations

Individuals with heterozygous protein C (PC) deficiency may have low normal PC levels. Treatment with warfarin decreases the levels of vitamin K-dependent factors including PC, and levels start to drop after six hours of warfarin treatment, not returning to pretreatment levels until generally two weeks after cessation of therapy. Elevated factor VIII levels can normalize the aPTT and effectively reduce PC levels. PC levels may be falsely low in patients with the factor VLeiden mutation. Additionally, PC levels can become depleted due to coagulation activation, limiting testing utility during the immediate convalescent period after a thrombotic event. This test should not be used for patients on thrombin inhibitors such as hirudin and argatroban.

Test Details

Methodology

Immunoassay (Chromogenic)

Biomarkers

Protein C

Protein

Protein C Activity

Expression • Quantitative (Continuous) (e.g., copies/mL, % expression)

LOINC Codes

Order Codes

27818-4 - Prot C Act/Nor PPP Chro

Result Codes

27818-4 - Prot C Act/Nor PPP Chro

Result Turnaround Time

2-3 days

Specimen

Plasma

Volume

1 mL

Minimum Volume

Not provided

Container

Blue-top (sodium citrate) tube

Collection Instructions

Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate. Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio. The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood.

Patient Preparation

Ideally, the patient should not be on anticoagulant therapy. Avoid warfarin (Coumadin®) therapy for two weeks prior to the test and heparin, direct Xa, and thrombin inhibitor therapies for about three days prior to testing. Do not draw from an arm with a heparin lock or heparinized catheter.

Storage Instructions

Freeze.

Causes for Rejection

Severe hemolysis; improper labeling; clotted specimen; specimen diluted with IV fluids; samples thawed in transit; improper sample type; sample out of stability