Novel homogeneous liposomal immunoassay for colorimetric estimation of serum IgG anticardiolipin antibodies.

Liposomes entrapping the dye sulforhodamine B were used to develop an assay for anticardiolipin antibodies (ACAs). In the presence of magnesium ions, IgG ACAs induced liposomal lysis and the resulting absorbance changes were dependent on the amount of ACAs present. The liposomal assay (y) showed similar intraassay imprecision and detection limit to an ELISA for IgG ACAs (x), with a correlation coefficient of 0.90 (y = 1.05x - 1.61). No correlation with ELISA IgM ACA measurements was observed. Although ELISA remains the method of choice, particularly in examining different ACA classes, the liposomal assay offers advantages of speed and potential for processing large numbers of samples for IgG ACAs. This may facilitate study of the significance of increased IgG ACAs in the groups of conditions with which they are associated, and perhaps enable more laboratories to perform the test.