[Use of an immunoenzyme microtechnic for quantitative determination of platelet-associated IgG in pediatrics. Acute idiopathic thrombocytopenia purpura and thrombocytopenia following exchange transfusion].

An enzyme linked immunoassay was developed using the microtiter system to measure platelet-associated IgG (PAIgG). The specificity of the assay was demonstrated in 6 children with acute idiopathic thrombocytopenic purpura (ITP): Elevated values of PAIgG (25-800 fg IgG/platelet) corresponded with low platelet counts. Complete remission was accompanied by normalization of PAIgG levels. Since immune destruction of platelets may be encountered in the development of neonatal postexchange thrombocytopenia, platelet counts and PAIgG levels were determined in pre- and postexchange samples from the recipient and in samples from the donor's blood. Eight double-volume exchange transfusions were studied in 7 newborns. Various patterns of interaction between donor and recipient were observed. Five donors proved to be thrombocytopenic, 3 of them had correspondingly high PAIgG levels, indicating immune destruction of donor platelets prior to transfusion. Three newborns had pre-existing immune thrombocytopenia before the exchange. Significant falls in platelet counts with concomitant rises in PAIgG were found following 2 out of 8 exchange transfusions. The quantitation of PAIgG by means of a micro enzyme linked immuno-assay is reliable and helpful in the detection of immune-mediated thrombocytopenia in all pediatric age-groups.