Elevated levels of PA IgG in thrombocytopenic patients are not related to the presence of microthrombocytes or megathrombocytes.

Platelet-associated (PA) IgG levels were measured on periph­ eral blood samples from 63 thrombocytopenic patients with the use of fluorescein isothiocyanate (FITC)-conjugated anti-IgG antibody. Test specificity was investigated by examining the influence of variables such as the platelet count in platelet-rich plasma (PRP), platelet loss after the assay procedure, and platelet size distribution (including the percentage of mi­ crothrombocytes and megathrombocytes) on the PA IgG levels. Additionally, PA IgG levels were compared with PA albumin levels and with levels of nonspecific adherence of FITC anti-IgG by the platelets to ascertain if elevated levels were specific. Elevated PA IgG levels showed only significant correlations (P < 0.05) with a mean platelet size below normal range and to increased PA albumin levels but not to PRP count, platelet loss after assay procedure, the percentage of microthrombocytes and megathrombocytes, and nonspecific adherence of FITC anti-IgG. (Key words: Platelet-associated IgG; Microthrombocytes and megathrombocytes; Thrombocy­ topenic patients) Am J Clin Pathol 1988; 89: 88-94