Platelet lactate dehydrogenase activity in systemic lupus erythematosus: correlation with anticardiolipin antibodies

OBJECTIVE: To evaluate lactate dehydrogenase (LDH) activity in platelet subpopulations in systemic lupus erythematosus (SLE) and to correlate platelet LDH activity with concentrations of anticardiolipin antibody (aCL). METHODS: Twelve female patients with SLE and 12 age matched female control subjects were studied. Platelets were separated on the Percoll gradient, their density values controlled by density marker beads. LDH activity was measured after platelet lysis, expressed as nU/fl. ELISA were used to measure levels of IgG and IgM aCL. RESULTS: A significant increase of LDH activity with a significant correlation to IgG and IgM aCL were found in small, light platelets with a volume < 5 mu 3 compared to large, dense platelets and to controls. LDH activity did not correlate with immunoglobulin classes, anti-DNA antibodies, and complement fractions in small and large SLE platelets. CONCLUSION: Our data suggest a possible chronic activation of subpopulations of small platelets in patients with SLE independent of thrombotic process. Low levels of aCL can mediate small platelet activation. Quantitative and qualitative analysis of the small, light platelets can serve a clinical diagnostic purpose as an in vivo platelet activation index in SLE.