Preservation of platelet receptors for platelet aggregating factor/von Willebrand factor by air drying, freezing, or lyophilization: new stable platelet preparations for von Willebrand factor assays.

The long-term preservation of platelet surface receptors for the platelet aggregating von Willebrand factor was achieved by freezing or drying of formaldehyde-fixed human platelets. Three separate procedures for platelet preservation were used: freezing at ?70°C, air-drying, and lyophilization. The preserved platelets were compared with the original fixed platelet preparations for reactivity in two types of tests for platelet aggregating von Willebrand factor, the ristocetin test with human plasmas and the platelet aggregating factor test with porcine and bovine plasmas. The new preparations of preserved platelets were equally reactive in both tests and showed no deterioration of activity on storage for periods of over one year. All of these preserved platelet preparations were satisfactory for use in both screening and bioassay procedures for the von Willebrand factor and provide a more convenient reagent than the original fixed platelet preparation.