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Protein S Antigen:Factor VII Antigen Ratio

CPT: 85230; 85305
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Expected Turnaround Time

4 - 7 days

Related Documents

For more information, please view the literature below.

Procedures for Hemostasis and Thrombosis: A Clinical Test Compendium

Specimen Requirements


Plasma, frozen


2 mL

Minimum Volume

1 mL


Blue-top (sodium citrate) tube


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 and carefully remove the plasma using a plastic transfer pipette, being careful not to disturb the cells. 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.

Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.

Storage Instructions


Patient Preparation

Do not draw from an arm with a heparin lock or heparinized catheter.

Test Details


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


This assay may not detect rare qualitative types of protein S deficiency.

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


Enzyme-linked immunosorbent assay (ELISA)

Additional Information

Because it is vitamin K dependent, the protein S level begins to decrease 60 hours after oral anticoagulant warfarin therapy is begun.6 When oral anticoagulant is stopped, its effects on protein S may be seen for up to two weeks or longer. For several days after surgery or a thrombotic event, the protein S levels may be diminished even in the absence of oral anticoagulants; during this period, assays cannot be used to establish a congenital deficiency. The total protein S antigen concentration assay:factor VII antigen concentration assay ratio may be used to determine a presumptive protein S deficiency in patients on oral anticoagulant therapy if clinical indications prevent suspension of therapy. A ratio ≤0.5 suggests protein S deficiency, however, deficiency cannot be ruled out when the ratio is ≥0.6, as a functional protein S deficiency will not be detected using this method.


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. 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. 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. 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. 10539100
6. Adcock DM, Bethel MA, Macy PA. Coagulation Handbook. Aurora, Colo: Esoterix−Colorado Coagulation; 2006.


Aiach M, Borgel D, Gaussem P, Emmerich J, Alhenc-Gelas M, Gandrille S. Protein C and protein S deficiencies. Semin Hematol. 1997 Jul; 34(3):205-216 (review). 9241706
Colman RW, Hirsh J, Marder VJ, et al, eds. Hemostasis and Thrombosis, Basic Principles and Clinical Practice. 4th ed. Philadelphia, Pa: Lippincott Williams and Wilkins; 2000.
Dahlback B. The protein C anticoagulant system: Inherited defects are a basis for venous thrombosis. Thromb Res. 1995 Jan 1; 77(1):1-43. 7701473


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
500530 Protein S/FVII Antigen Ratio 500531 Protein S Antigen, Total % 27823-4
500530 Protein S/FVII Antigen Ratio 500532 Factor VII Antigen** % 49870-9
500530 Protein S/FVII Antigen Ratio 500533 Protein S Ag/FVII Ag Ratio** ratio 18345-9

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