Inter-assay variation in antiphospholipid antibody testing.

We evaluated inter-assay variation in anticardiolipin antibody status, comparing three centres, and using different assays among 36 women with recurrent miscarriage and 26 controls. There was no more agreement between the laboratories than would be predicted on the basis of chance for IgM and only fair agreement among the laboratories for IgG. None of the tests were significantly more likely to be positive in the cases compared with the controls.