FACTOR VIII RISTOCETIN COFACTOR, RISTOCETIN COFACTOR, VON WILLEBRAND FACTOR ACTIVITY
Ristocetin-induced Platelet Aggregation with normal platelets and patient plasma
Specimen Collection Details
One 4.5 mL light blue top tube (sodium citrate). Collect by careful venipuncture to avoid tissue fluid contamination or hemolysis. Do not use needles smaller than 23 gauge. Fill tube to maximum draw, at least 90% full. Mix by gentle inversion. Call the Special Coagulation Department (541-687-2134 x4612) when urgent testing is needed in order to assure STAT testing.
Due to short stability specimens must either be sent STAT to arrive at the laboratory within 4 hours, or sent frozen. It STAT, refrigerate and keep capped in original tube. Call for STAT pick-up. For standard delivery, centrifuge to produce platelet poor plasma (at least 1700 X G for 15 minutes) and using a plastic pipette, transfer the top 2/3 of the plasma into a plastic vial. Label with patient name, I.D. number, test, and “citrated plasma.” Freeze immediately. Send to the laboratory within 7 days. If multiple tests are ordered, freeze a separate aliquot for this test.
4 hours refrigerated, or 7 days frozen.
5 mL whole blood or 2 mL plasma.
1.8 mL whole blood or 0.5 mL plasma.
Original tubes refrigerated if STAT, or plasma frozen on dry ice in Styrofoam container.
Von Willebrand’s Factor is an ”acute phase reactant.” As a result, the Ristocetin Cofactor level increases during pregnancy, infection, and inflammation. Patients should not be screened for Von Willebrand’s disease during these conditions, since abnormal results may transiently normalize and mask disease. See also:Coagulation Study, von Willebrand Disease (25770).
Visible fibrin; moderate to marked hemolysis; specimen received in laboratory beyond stated stability.