Inter-laboratory variability of anti-beta2-glycoprotein I measurement. A collaborative study in the frame of the European Forum on Antiphospholipid Antibodies Standardization Group.
Inter-laboratory variability of anti-beta2-glycoprotein I antibody measurements (IgG and IgM) was investigated in the frame of the European Forum on Antiphospholipid Antibodies and its Standardization Group. Twenty-eight samples from patients with autoimmune diseases, two samples from blood donors and a set of six calibrators obtained by dilution with normal plasma of a pool of patient samples were sent to 21 European centers. Six of them used commercial kits and the others home-made assays. Marked differences in the steepness of the calibration curves obtained with the calibrator provided were observed. The standard deviations of sample measurement were high. Cut-off of positivity varied from 7 to 90 Forum Units (FU) for IgG and from 10 to 138 FU for IgM, whereas the rate of positivity varied from 50 to 93% for IgG and from 13 to 70% for IgM. No clear relationship between cut-off values and positivity rate could be established for either isotype. Adopting a common cut-off did not markedly improve the overall agreement between centers in positive/negative sample classification. Because of the majority of low positive samples, excellent concordance between centers (as defined by kappa values from 0.8 and 1) occurred only in 13% of cases for IgG and in 6% of cases for IgM, because many selected samples were low-positive. Despite the large variability of anti-beta2-glycoprotein I measurements between centers, the agreement on results with high- and medium-positive samples was good.
Reber
Guido
G
Haemostasis Unit, Geneva University Hospital, Switzerland. guido.reber@hcuge.ch
Schousboe
Inger
I
Tincani
Angela
A
Sanmarco
Marielle
M
Kveder
Tanja
T
de Moerloose
Philippe
P
Boffa
Marie-Claire
MC
Arvieux
Josiane
J
D001323:Autoantibodies / Q000097:blood*; D001327:Autoimmune Diseases / Q000097:blood / Q000276:immunology; D002138:Calibration; D003299:Cooperative Behavior; D006023:Glycoproteins / Q000276:immunology*; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007075:Immunoglobulin M / Q000097:blood; D015588:Observer Variation; D011933:Reagent Kits, Diagnostic / Q000592:standards; D012015:Reference Standards; D012698:Serologic Tests / Q000379:methods / Q000592:standards; D053482:beta 2-Glycoprotein I
D001323:Autoantibodies; D006023:Glycoproteins; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D011933:Reagent Kits, Diagnostic; D053482:beta 2-Glycoprotein I