Lab Test

Protein C Activity

Protein C Functional , Antrim #26250, EPIC: LAB5205, SOFT: PCACT


  • The patient should be off warfarin for at least two weeks prior to specimen collection.
  • Specimens with hematocrit values greater than 55% must have anticoagulant adjusted. Specimens must be re-collected using a specified whole blood to sodium citrate ratio. Contact the performing Laboratory for specific instructions.

Specimen Collection Criteria

Collect: A minimum of two (2) Light Blue-top Becton-Dickinson 3.2% Sodium Citrate tubes.


Physician Office/Drawsite Specimen Preparation

For optimal results, maintain whole blood specimen at room temperature (20-26°C or 68-78.8°F) prior to transport. Transport whole blood to the Laboratory within 4 hours of collection. If transport within 4 hours is not possible, the following procedure must be followed for accurate results:

  1. Centrifuge the capped tubes at 1500 x g for 15 minutes.
  2. Transfer plasma with plastic pipette into a plastic polypropylene centrifuge tube, cap and centrifuge an additional 15 minutes at 1500 x g to obtain platelet poor plasma (PPP) which has a platelet count less than 10 bil/L. Plasma with a platelet count of less than 10 bil/L is critical for accurate results.
  3. Immediately remove only the top two-thirds of the PPP and transfer into two (2) plastic transport tubes.
  4. Freeze (-20°C/-4°F or below) the PPP immediately.
  5. Transport frozen on DRY ICE. Specimen must remain frozen during transport. 

Preparation for Courier Transport

Transport: Whole blood at room temperature (20-25°C or 68-77°F), or plasma obtained through the process listed above, frozen (-20°C/-4°F or below).

Rejection Criteria

  • Glass tubes and 3.8% Sodium Citrate tubes.
  • Specimens that are clotted or grossly hemolyzed.
  • Inappropriate specimen volume.
  • Thawed or partially thawed specimens.


Minimum once per week.
Results available within 7 days, or within 14 days if Protein C antigen test is required.

Reference Range

Protein C Activity
Normal: 70 - 185%.

Protein C Antigen
0-10 days: 0-50%
greater than 10 days: 72-160%

Test Methodology

Protein C Activity
Change in Optical Absorbance (IL ACL TOP Series).

Protein C Antigen
Enzyme Immunoassay.


  • Highly elevated Factor VIII yields lower protein C values. The presence of a mutation of Factor V Leiden may also yield a lower protein C. Heparin up to 2 U/mL does not interfere with this assay. Lupus anticoagulants may interfere causing higher protein C concentrations.
  • Protein C deficiency is a cause of inherited thrombosis. Acquired protein C deficiency occurs in disseminated intravascular coagulation (DIC), liver disease, vitamin K deficiency, and in neonates, and can result in various thrombotic states. Complete absence of protein C can lead to fatal thrombosis in neonates.
  • Increased levels of protein C may be seen in patients with diabetes, nephrotic syndrome, pregnancy, and oral contraceptive use.
  • If a decreased Protein C activity is obtained and the patient is not on Coumadin, a Protein C antigen (total and free) will also be performed.

Clinical Utility

Vitamin K dependent Protein C is an inhibitor of coagulation. In the presence of cofactor, Protein S, it neutralizes the activity of activated Factor V and VIII. This assay aids in the diagnosis of patients with thrombosis, especially venous thrombosis in young adults. It also aids in the study of patients with hypercoagulable state.

CPT Code

85303. Add 85302 if antigen is performed.

Test Codes

Antrim #26250, EPIC: LAB5205, SOFT: PCACT

Last Updated


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This directory currently reflects information only for specimens collected and/or processed at the
Farmington Hills, Grosse Pointe, Royal Oak, and Troy campuses.