Interference of lysophosphatidylcholine in hormone radioimmunoassays

The interference of synthetic and naturally occurring detergents in immunoassays is well documented. In the present study, we evaluated the effect of lysophosphatidylcholine (LPC) and found that the lysophospholipid interfered with formation of the antigen-antibody complex in hormone immunoassays. In the presence of LPC (100 mumol/L), progesterone was overestimated by 29%. Furthermore, physiological concentrations of LPC (140 mumol/L) interfered with the assays of cortisol, progesterone, and aldosterone, resulting in overestimations of 35%, 30%, and 27%, respectively. The addition of albumin decreased the interference by LPC to 7% in the assay of cortisol and progesterone when the LPC:albumin ratio was unity. Adding cholesterol (100 mumol/L) also reduced by 50% the interference induced by LPC. Finally, treating plasma to increase the endogenous LPC concentration also resulted in interference in the cortisol assay. Thus, interpretation of the results of these assays should take into consideration the endogenous serum albumin:LPC ratio.