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For hours, walk-ins and appointments.Test Includes
Protein C antigen; factor VII antigen; protein C:factor VII ratio
Expected Turnaround Time
3 - 6 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Related Documents
Specimen Requirements
Specimen
Plasma, frozen
Volume
1 mL
Container
Blue-top (sodium citrate) tube
Collection
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.
Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.
Storage Instructions
Freeze.
Causes for Rejection
Hemolysis; clotted specimen; specimen contaminated with heparin (ie, drawn with blood gases); samples containing fibrin clots; specimens received thawed for more than 24 hours
Test Details
Use
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.
Limitations
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.
Methodology
Enzyme-linked immunosorbent assay (ELISA)
Reference Interval
0.5:2.2 ratio
Additional Information
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.
Footnotes
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
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 500534 | Protein C Ag/FVII Antigen | 500535 | Protein C Antigen | % | 27820-0 | |
| 500534 | Protein C Ag/FVII Antigen | 500532 | Factor VII Antigen** | % | 49870-9 | |
| 500534 | Protein C Ag/FVII Antigen | 500536 | Protein C Ag/FVII Ag Ratio** | ratio | 27438-1 |
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