Decreased platelet serotonin levels in systemic lupus erythematosus.

Platelet serotonin levels were measured in 41 patients with systemic lupus erythematosus (SLE) and 36 normal controls. SLE patients had significantly lower mean serotonin levels (243 +/- 131 versus 414 +/- 175 ng/10(9) platelets, P less than 0.001); the lowest levels occurred in those patients with active disease. No differences in mean platelet serotonin levels were found when we compared patients with or without a history of renal disease, thrombocytopenia, or neuropsychiatric involvement. Decreased release of platelet granule constituents, as measured by plasma levels of the alpha-granule protein, beta-thromboglobulin.