Protein C Activity : 1000746

The aliquot must remain frozen. Freeze thaw cycle will adversely affect specimen integrity. CRITICAL FROZEN: Separate specimens must be submitted when multiple tests are ordered.

Test Code
PRTCA or 1000746

Alias/See Also
Functional Protein C

CPT Codes

Blue top tube, 3.2% sodium citrate.
• Obtain venous blood by clean venipuncture. Avoid slow-flowing draws and/or traumatic venipunctures as either of these may result in an activated or clotted specimen. Do not use needles smaller than 23 gauge. Do not leave the tourniquet on for an extended length of time before drawing the sample.
• A pilot tube (non-additive or light blue tube) before drawing coagulation specimens in light blue vacuum tubes is only necessary when using a butterfly blood collection set as this will cause reduced draw volume in the first tube. Discard the pilot tube.
• Fill light blue tubes as far as vacuum will allow and mix by gentle inversion. Exact ratio of nine parts blood to one part anticoagulant must be maintained. Inadequate filling of the sample tube will alter this ratio and may lead to inaccurate results. Patients who have hematocrit values above 55 percent should have the anticoagulant adjusted to maintain the 9:1 ratio. Use the following formula to determine the amount of anticoagulant to use: [(100 – Hct) / (595 – Hct) ]* total volume = amount of anticoagulant required.
• After collecting the blood, examine the tube to ensure that it is filled to within 90% of the fill line.
• Note: Specimens containing heparin should not be used for coagulation studies. If possible, stop heparin therapy before the draw to avoid contamination. Heparin interferes with most clotting assays. If heparinized line must be used to obtain the sample, flush line with 5mL saline and discard the first 5 mL of blood drawn into a syringe, or 6 “dead space” volumes of the line.

Transport Container
Blood collected in 3.2% sodium citrate (light blue top tube). Proper blood to anticoagulant ratio is required. The tubes must be at a 100 ± 10% fill volume to maintain the correct ratio. Centrifuge light blue-top tube at 1500 g for no less than 15 minutes or speed/time to consistently yield platelet-poor plasma (<10,000/µL). Using a plastic pipette, remove plasma, taking care to avoid the WBC/platelet buffy layer, and place into a plastic transport tube (Min. 1 mL). Immediately freeze the aliquot and ship on dry ice.

Transport Temperature

Specimen Stability
After separation from cells: Ambient: Unacceptable; Refrigerated: Unacceptable; Frozen: 30 days

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Hemolysis; marked icterus; marked lipemia; received thawed; received refrigerated; received room temperature


Setup Schedule
Tuesday & Thursday

Report Available
1-6 days

Reference Range
67-144 %

Clinical Significance
Determination of functional activity of Protein C in plasma via clotting-based assay.

Protein C is a vitamin-K-dependent coagulation inhibitor, which regulates the activity of coagulation factors V and VIII. Congenital heterozygous deficiency leads to a high, age-dependent incidence of venous thromboses. An acquired deficiency may be due to vitamin K deficiency, e.g., as a result of absorption disturbances or oral anticoagulant therapy. In vitamin K deficiency, other vitamin K-dependent coagulation factors are also diminished in activity and therefore the risk of thrombosis under these conditions is small. Due to the short half-life of Protein C, the induction of oral anticoagulant therapy may lead to very low levels of Protein C activity with the risk of coumarin necroses.

Protein C Reagent detects essential functions of Activated Protein C such as proteolysis of Factor V and VIII and interaction with Protein S. Protein C synthesized in conditions of vitamin K deficiency is not detected and therefore the Protein C activity found is lower than with chromogenic methods.


1. Highly elevated activities of coagulation Factor VIII yield lowered Protein C values as
a result of the measurement principle (modified APTT) used.

2. The presence of a mutation of Factor V at the protein Ca cleavage site (Factor V Leiden)
may likewise lead to diminished recovery of Protein C.

3. Heparin up to a concentration of 2 U/mL does not interfere.

4. Lupus anticoagulants are reported to interfere and may lead to prolonged
clotting times, thus indicating apparently higher Protein C concentrations.

5. Hemolyzed specimens are not suitable for Protein C determination.

Performing Laboratory
med fusion

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.