Screening test for the factor V Leiden gene mutation and other causes of activated protein C resistance

• Ideally, the patient should not be on anticoagulant therapy
• Avoid warfarin (Coumadin®) therapy for two weeks prior to the test and heparin (direct Xa and thrombin inhibitor therapies) for about three days prior to testing

Lt blue (NaCit)

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

Citrated plasma samples should be collected by double centrifugation. Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate. Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio. 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, except when using a winged blood collection device (ie, "butterfly"), in which case a discard tube should be used. 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.

If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted.

1. Centrifuge within 30 minutes of collection.
2. Centrifuge for 10 minutes and carefully remove ²/₃ of the plasma using a plastic transfer pipette, being careful not to disturb the cells.
3. Deliver to a plastic transport tube, cap, and recentrifuge for 10 minutes.
4. Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube.
5. Transfer the plasma into a Screw-cap polypropylene frozen transport vial/tube - 4mL (LabCorp).
6. Freeze immediately and maintain frozen.

Screw-cap polypropylene frozen transport vial/tube - 4mL (LabCorp)

Frozen - 28 days

• Freeze/thaw cycles - stable x3

• Gross hemolysis
• Clotted specimens
• Specimens that have thawed in transit
• Tubes < 90% full
• Improperly labeled specimen
• Specimen collected in tube other than 3.2% citrate

This assay measures the effect of adding aPC on the activated partial thromboplastin time (aPTT) of the patient sample.8,9 An aPTT is performed twice, once with and again without added aPC. The ratio of the two clotting times is reported. The patient sample is diluted with factor V-deficient plasma. This serves to correct for any factor deficiencies in the patient sample and allows the test to be used for patients on oral anticoagulants. The reaction mixture also contains a heparin neutralizer to allow this test to be performed on patients receiving heparin therapy.

2.2 - 3.5 ratio