Protein C Antigen/Factor VII Antigen

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Turnaround Time: 3 - 6 days
CPT Code:

85302, 85230

Test Type: 1 mL Plasma, frozen
Reference Range:

0.5:2.2 ratio


This assay is used to obtain a presumptive diagnosis of protein C deficiency while a patient is receiving antivitamin K therapy. Use of this assay is discouraged.

The extremely rare presence of antirabbit antibodies in certain subjects leads to aberrant results.

This procedure may be considered by Medicare and other carriers as an investigational and, therefore, may not be payable as a covered benefit for patients.

Protein C (PrC) and factor VII (F VII) are vitamin K-dependent factors and may be decreased in patients on stable antivitamin K (warfarin) therapy. By calculating a PrC:VII ratio, a tentative diagnosis of PrC deficiency can be made in those patients receiving stable antivitamin K therapy. A decreased PrC:VII antigen ratio is indicative of a protein C deficiency; however, a final diagnosis of protein C deficiency should not be made until and individual has been removed from warfarin therapy for a minimum of two weeks and then testing repeated. The kindred of protein C deficient individuals should be screened for deficiency both to confirm its hereditary nature and to assess thrombotic risk to family members.

1. Adcock DM, Kressin DC, Marlar RA. Effect of 3.2% vs 3.8% sodium citrate concentration on routine coagulation testing. Am J Clin Pathol. 1997Jan; 107(1):105-110. PubMed 8980376

2. Reneke J, Etzell J, Leslie S, Ng VL, Gottfried EL. Prolonged prothrombin time and activated partial thromboplastin time due to underfilled specimen tubes with 109 mmol/L (3.2%) citrate anticoagulant. Am J Clin Pathol. 1998 Jun; 109(6):754-757. PubMed 9620035

3. National Committee for Clinical Laboratory Standardization. Collection, Transport, and Processing of Blood Specimens for Coagulation Testing and General Performance of Coagulation Assays; Approved Guideline. 5th ed. Villanova, Pa: NCCLS; 2008. Document H21-A5:28(5).

4. Gottfried EL, Adachi MM. Prothrombin time and activated partial thromboplastin time can be performed on the first tube. Am J Clin Pathol. 1997 Jun; 107(6):681-683. PubMed 9169665

5. McGlasson DL, More L, Best HA, Norris WL, Doe RH, Ray H. Drawing specimens for coagulation testing: Is a second tube necessary? Clin Lab Sci. 1999 May-Jun; 12(3):137-139. PubMed 10539100

Collection Details:

Collection Instructions:

Blue-top (sodium citrate) tube.

Citrated plasma samples should be collected by double centrifugation. Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.1 Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio.2,3 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples.4,5 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternate anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells. Deliver to a plastic transport tube, cap, and recentrifuge for 10 minutes. Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube. Transfer the plasma into a LabCorp PP transpak frozen purple tube with screw cap (LabCorp N° 49482). Freeze immediately and maintain frozen until tested. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.