Quantification of platelet-bound IgG by 125I-Staphylococcal protein A in
immune thrombocytopenic purpura and other thrombocytopenic disorders
GM Shaw, J Axelson, JG Maglott and AF LoBuglio
In this report we describe the use of an 125I-Staphylococcal protein A
(SPA) assay to measure platelet-bound IgG in the evaluation of 62
thrombocytopenic patients. Platelets from 150 normal subjects were found to
bind 146 +/- 112 molecules of SPA per platelet (mean +/- 2 SD). Nineteen of
20 patients with untreated immune thrombocytopenia had platelet IgG values
above this range, with 15 of 20 having values above 1,000 molecules of SPA
per platelet. Patients with immune thrombocytopenic purpura by clinical
criteria, but who had failed conventional therapy (corticosteroids or
splenectomy), had a wide range of platelet IgG levels: 4 of 20 had normal
values, 6 of 20 had minimally elevated levels in the range seen with
nonimmune thrombocytopenia, and 10 of 20 had much higher values. Fifteen
patients with thrombocytopenia of apparent nonimmune origin and 7 others
with chronic stable thrombocytopenia of unknown etiology were found to have
platelet IgG levels within or only slightly above the normal range. Because
of its simplicity, accuracy, and clinical correlation, the 125I- SPA assay
provides an important new approach for studying platelet IgG in
thrombocytopenic states. The data obtained with this technique are similar
to those found in immune hemolytic anemia and suggest that the
platelet-bound IgG so measured has pathophysiologic relevance in immune
thrombocytopenic purpura.
Volume 63,
Issue 1,
pp. 154-161,
01/01/1984
Copyright © 1984 by The American Society of Hematology
