Platelet heterogeneity based on lactic dehydrogenase activity.

Mean lactic dehydrogenase (LDH) activity of human platelets is about 5 nU/platelet; expressed on a cell volume basis, it is 0.5 nU/fl. Platelet separation by means of centrifugation on a Percoll discontinuous gradient gives different subpopulations with a clear-cut change of LDH at a mean platelet volume (MPV) of about 6 fl. The LDH content of platelets with a MPV > 6 fl is constant (about 0.5 nU/fl), while that of small platelets (3 < MPV < 6 fl) is inversely correlated with the MPV and reaches a value of 1.5-2.0 nU/fl. Because small platelets are granule-depleted, we suggest that platelet LDH activity be considered as an in vivo activation index.