A Simplified Method for Measuring the Binding Capacity of Sex Hormone-Binding Globulin in Human Serum and Its Clinical Application

Abstract

A simple and reliable method for determining the binding capacity of the sex hormone-binding globulin (SHBG-BC) in human serum is described. The principle of this method is to saturate the SHBG binding sites with dihydrotestosterone (DHT) and measure the amount of SHBG-bound steroid. Endogenous steroids are initially removed from the serum samples by adsorption on dextran-coated charcoal. The samples are subsequently equilibrated with a mixture of a known amount of tritium-labeled and unlabeled DHT. The unbound steroid is removed by dextran-coated charcoal incubated at 4°C, and the mass of bound DHT is determined from the known specific activity of the added steroid. The intraassay and inter-assay coefficient of variation of this assay method is less than 6.2% and 7.5%, respectively. Forty serum samples can be assayed in duplicate in a working day.
The mean values of SHBG-BC, expressed as pg DHT bound per 100ml serum, were 1.56±0.33 (SD) in 6 adult men aged 20-40 and 2.05±0.75 in 37 adult women aged 20-36. Higher levels (1.75±0.40) were found in 10 older men aged 65-80. In contrast, SHBG-BC (1.80±0.30) in postmenopausal women (ages 52-62) was lower than that in the reproductive age group of women. No significant variations in SHBG-BC were observed during the normal menstrual cycle. The levels of SHBG-BC rose progressively in pregnancy to 9-10 times those in the normal non-pregnant women. In 4 women with polycystic ovarian disease and 2 hirsute women, SHBG-BC levels were lower (means : 1.63 and 0.75, respectively), while patients with 1st and 2nd grade amenorrhea showed levels similar to those in the reproductive women.