Platelet markers of suicidality.

Six serotonergic measures in blood platelets, Km and Vmax of serotonin (5-HT) uptake, Kd and Bmax of 3H-imipramine binding, 5-HT content, and MAO activity, were measured in depressed and other psychiatric patients and related to Hamilton Depression Scale suicide ratings. Km was negatively correlated with the suicide rating while Kd was positively correlated with it. Multivariate analyses showed that Km, Kd, Vmax, and MAO activity were significant predictors of Hamilton Depression Scale suicide ratings. Low platelet MAO activity was present in seven nondepressed females who had made suicide attempts in the current episode. The direction of the association between the platelet measures and suicide ratings indicated diminished presynaptic serotonergic activity in patients with high suicide ratings, if the platelet findings could be extrapolated to 5-HT nerve terminals.