A B S T R A C T A sensitive and precise competitivedisplacement double-antibody radioimmunoassay was developed for the human plasma enzyme lecithincholesterol acyltransferase (LCAT; EC 2.3 1.43). The ability of plasma from various animal species to displace labeled human LCAT from goat anti-human LCAT could be ranked in the following order: man and sheep > nonhuman primates > cat or dog > pig > rabbit or guinea pig > mouse > rat. Normolipidemic subjects had levels of LCAT of 6.14+0.98 ,ug/ml (mean± SD, n = 66). Subjects with dysbeta-lipoproteinemia had the highest plasma LCAT levels (7.88±0.39 ,ug/ml, n = 7, P < 0.05), followed by hypercholesterolemic subjects (7.00±1.30, n = 41) and hypertriglyceridemic subjects (6.96±1.3, n = 10). LCATdeficient subjects had the lowest enzyme levels (0.89, 0.83, and 0.05 ,ug/ml, respectively, and two subjects with no detectable enzyme). Males had lower LCAT levels (6.42±1.05 ,ug/ml, n = 90, for all subjects; 5.99+1.03, n = 44, for normolipidemics) than females (7.01+1.14, n = 34, forall subjectsP < 0.01; 6.44+0.79, n = 22, for normolipidemics, P < 0.01). LCAT levels correlated significantly with total cholesterol (males, r = 0.384, P < 0.001; females, r = 0.519, P < 0.002); and total triglyceride (only in females, r = 0.512, P <0.002). LCAT levels in females correlated inversely with HDL cholesterol (r = -0.341, P < 0.05) and apoprotein D (r = -0.443, P < 0.02), but no such relationship existed in males.
