Specimen Requirements



Specimen Requirement

Collect light blue top sodium citrate. The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. Centrifuge and pipette plasma to a screw top plastic vial, centrifuge again, then pipette plasma (1 mL required) to a second screw top plastic vial. Indicate plasma from light blue on the transport tube, freeze immediately and ship on dry ice.

Patient Preparation:
Avoid warfarin (Coumadin®) therapy for two weeks and heparin therapy for two days prior to the test. Do not draw from an arm with a heparin lock or heparinized catheter.


The patient plasma is added to PS-depleted normal plasma with normal levels of all factors but PS. The mixture is supplemented with excess aPC and factor V is then added. The extent of prolongation of the time to clot formation after calcium chloride is added is proportional to plasma PS activity.


Critical Frozen

Reference Range

By Report*


2-3 days

Clinical Use

Confirmation and characterization of protein S (PS) congenital deficiency

Test Code