Routine ultramicro-measurement of human growth hormone in plasma by solid-phase radioimmunoassay.

Abstract

A method for the ultramicro-measurement of human growth hormone (HGH) in plasma based on the solid-phase radioimmunoassay (RIA) using antibody-coated disposable microtiter trays was described. This method is simple, rapid and inexpensive, and particularly useful for ultramicro-measurement of plasma HGH levels in large numbers of plasma samples.The lower limit of sensitivity for purified HGH was 25pg/ml (P<0.05). The precision of the measurement of HGH in plasma has been calculated, and the quantitative sensitivity of the method derived from the results given by its routine use was 56.8pg/ml (P<0.05). The HGH level of normal pooled plasma in 10 replicates was 1, 515pg/ml (±126;1SD), and the coefficient of variation was 8.3%.The mean basal plasma HGH level after an overnight fasting in 23 normal males was 2, 100pg/ml (±1, 491; 1 SD) by this method and 2, 036pg/ml (1, 643; 1 SD) by double-antibody RIA, and in 23 normal females, 2, 589pg/ml (±1, 189; 1 SD) and 3, 300 pg/ml (±1, 690; 1 SD) respectively; there was no statistically significant difference between the basal HGH level obtained from this method and that from double-antibody RIA in normal subjects. On the other hand, the mean basal plasma HGH level after an overnight fasting in 21 hypopituitary patients was 484pg/ml (±282; 1 SD) by this method, and this value was significantly lower (P<0.001) than 1, 376pg/ml (±498; 1 SD) by double-antibody RIA. These data show that determination of basal plasma HGH levels by this method is of much value in the diagnosis of hypopituitarism.