Shape and functional properties of human platelets washed with acid citrate.

Acid citrate pH 6.5 protects human platelets from activation during washing at room temperature. Platelets suspended in media containing citrate pH 6.5 have an extra-flat disc shape. Citrate at pH 6.5 also inhibits the ADP-induced shape change. When warmed to 37 degrees C and suspended into the test medium of pH 7.4, the washed platelets aggregate with low concentrations of ADP or epinephrine in the presence of fibrinogen and Ca2+. The morphological and functional quality of platelet concentrates (6 X 10(6) microliter-1) stored in acid citrate pH 6.5 is maintained for at least 6 h at room temperature.