02 November 1999
In order to evaluate the in vitro bioactivity of LH during normal puberty compared to LH immunoactivity measured in a highly sensitive immunoassay, blood plasma samples from healthy children were analyzed in a mouse Leydig cell assay (MLCA). Blood samples were obtained from 60 healthy girls and boys during normal pubertal development. Samples were taken on two occasions with a 1-year interval. Three daytime samples and three nighttime samples were analyzed. The correlation of the LH immunoradiometric assay (IRMA) activity with the LH activity in the MLCA varied from 0.60 to 0.96 in the different pubertal stages. During pubertal development, a gradually increase in the activity of LH in both the IRMA and MLCA was found. The ratio of the in vitro bioactivity compared to the immunoreactivity (B/I ratio) did not change significantly during puberty: it was 0.84 (SD 0.58) and 0.66 (SD 0.40) during the first and second sampling period in girls and 0.88 (SD 0.38) and 0.91 (SD 0.46, NS) in the boys. The B/I ratio of LH does not change during puberty. With a high sensitivity and specificity, measurement of LH by IRMA gives representative measurements of the LH in vitro bioactivity in children during pubertal development.