Variation with age in the levels of sex-steroid-binding plasma protein as determined by radioimmunoassay.

A radioimmunoassay for human sex-steroid-binding plasma protein (SBP) was developed. With this assay, SBP was determined in sera of 138 normal men and 169 non-pregnant women, ranging in age from 11 to 87 years. The results indicate that SBP levels in both sexes increase gradually with age up to mid-eighties, that the average levels in mid-eighties are approximately twice those in early twenties, and that the average levels in women are about twice as high as those in men of corresponding age. These results may also account for the discrepancies in the previous papers regarding the normal blood levels and sexual difference of SBP in adult men and women.