Platelet-associated IgG in thrombocytopenia: a comparison of two techniques.
The results obtained in the analysis of 130 thrombocytopenic patients with a radioimmunoassay (RIA) for platelet-associated IgG (PA-IgG) and the platelet suspension immunofluorescence test (PIFT) were compared. The RIA was positive in 33 of 41 (82.9%) patients with idiopathic thrombocytopenia (ITP) and in 51 of 79 (64.4%) patients with secondary thrombocytopenia (STP). The PIFT was positive in 37 of the 41 (90.2%) ITP patients and in 57 of the 79 (72.2%) STP patients. Sensitivity and specificity for the diagnosis of ITP of both tests were comparable: 82.9 and 40.9% for the PA-IgG(RIA) and 90.2 and 36.7% for the PIFT. A significant positive correlation was observed between the mean amount of PA-IgG measured and the height of PIFT scores with anti-IgG. Of 38 discrepancies between PA-IgG(RIA) and PIFT with anti-IgG, 15 were due to borderline results, 17 were associated with abnormal platelet-size distribution and 20 were associated with occurrence of IgM antibodies. These results suggest influences of platelet fragments and/or aggregates on accurate measurement of PA-IgG. Both fragments and aggregates escape from accurate platelet counting, while their contribution to the total IgG content remains. Therefore, a falsely elevated PA-IgG (RIA) may be measured.
Vos
J J
JJ
Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, Academic Medical Centre of the University of Amsterdam.
Huisman
J G
JG
van der Lelie
J
J
von dem Borne
A E
AE
D000328:Adult; D000906:Antibodies / Q000032:analysis; D001792:Blood Platelets / Q000378:metabolism*; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis*; D007075:Immunoglobulin M / Q000276:immunology; D008297:Male; D008875:Middle Aged; D010976:Platelet Count; D011863:Radioimmunoassay; D013921:Thrombocytopenia / Q000097:blood* / Q000175:diagnosis
D000906:Antibodies; D007074:Immunoglobulin G; D007075:Immunoglobulin M