Presence of elevated circulating levels of LH during the pre-menstrual period in some copper IUD users and the possibility of their confusion with hCG.

A heterologous radioimmunoassay (RIA) capable of discriminating between LH and hCG was used to measure LH levels in sera obtained during the pre- and post-menstrual periods from 80 women bearing copper intrauterine contraceptive devices (IUD). hCG levels in these samples were also estimated by use of a homologous beta-hCG radioimmunoassay and a radioligand-receptor assay. Only two IUD users during the pre-menstrual period had detectable, but low hCG levels. However, LH levels, as estimated by specific RIA, in the serum of these two women were elevated to a level that would cause detection at low levels in the hCG assays. The data thus provide direct evidence to indicate that the positive hCG levels observed by others during the pre-menstrual period in some copper IUD users could be due to the interference in hCG assays by elevated LH.