Laboratory abnormalities in thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura is an uncommon disorder that requires p rompt recognition and intervention to prevent death. To date, information r egarding the classic laboratory abnormalities in the disease has been deriv ed from small numbers of patients whose laboratory tests have been done at many different sites. We report the laboratory findings in 135 patients who presented with thrombotic thrombocytopenic purpura to 17 Canadian centres. 50 men and 85 women had a mean platelet count of 25.3 +/- 10.4x10(9)/l. Th e initial platelet count correlated with mortality; 32% of patients with a platelet count of 20 x 10(9)/l or less died compared with 18% of patients w ith a platelet count >20x10(9)/l (P=0.058). The platelet-associated IgG was elevated in 88% at presentation whereas the indirect platelet suspension i mmunofluorescence test was positive in only 18%. 93% of the sera showed rea ctivity against platelets following protein blotting. All sera tested also showed reactivity against endothelial cells. Immune complexes were seen in all patients, whereas the platelet aggregating factor was detected in 59%, Although the von Willebrand factor was elevated in the majority of patients at entry, the multimer pattern was variable and showed no predictive patte rn. Renal dysfunction was common (18%).