Protein S Antigen:Factor VII Antigen Ratio
Use
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.
Special Instructions
Because it is vitamin K dependent, the protein S level begins to decrease 60 hours after oral anticoagulant warfarin therapy is begun. When the oral anticoagulant is stopped, its effects can be observed for up to two weeks or longer, complicating the interpretation of results. The test's results should be carefully surrounded with clinical context, especially when dealing with cases where the suspension of anticoagulant therapy is not an option.
Limitations
This assay may not detect rare qualitative types of protein S deficiency. It is considered investigational by Medicare and other carriers, and therefore may not be payable as a covered benefit for patients. The effects of warfarin on protein S levels and the influence of recent surgery or thrombotic events further limit its reliability for detecting congenital deficiencies.
Methodology
Immunoassay (ELISA)
Biomarkers
LOINC Codes
- 27823-4
- 49870-9
- 18345-9
Result Turnaround Time
4-7 days
Related Documents
For more information, please review the documents below
Specimen
Plasma
Volume
2 mL
Minimum Volume
1 mL
Container
Blue-top (sodium citrate) tube
Collection Instructions
Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate. Evacuated collection tubes must be filled to completion. Mix immediately by gentle inversion at least six times. No discard tube is needed before collection of coagulation samples. Noncitrate tubes should be collected before citrate tubes when noncitrate tubes are required. Centrifuge and transfer plasma into a Labcorp PP transpak frozen purple tube with a screw cap. Freeze immediately and maintain frozen until tested.
Patient Preparation
Do not draw from an arm with a heparin lock or heparinized catheter.
Storage Instructions
Freeze.