REPRESENTATIVENESS OF A SINGLE POINT PLASMA TESTOSTERONE LEVEL FOR THE LONG-TERM HORMONAL MILIEU IN MEN

To test the reliability of a single plasma testosterone (T) or dihydrotestosterone (DHT) level, respectively, as a parameter of the long term hormonal milieu, plasma T and DHT levels were measured eight times, over a period of 50 weeks, in 169 middle-aged and elderly men with symptomatic benign prostatic hyperplasia, who where otherwise healthy. The results show an excellent correlation (r = 0.849) between plasma androgen levels at first sampling and the mean of the 7 samples taken subsequently over 1 yr. Of the 22 subjects with plasma testosterone levels below the lower limit of normal (10 nmol/L) at first sampling, none had an annual plasma T value greater than 13.5 nmol/L, i.e. the annual mean was also below the normal limit or in the low normal range, whereas of the 18 subjects with a T level at first sampling above 25 nmol/L (+/- 90th percentile), none had a mean plasma T level below 19.0 nmol/L (70th percentile). Similar results were obtained for DHT. When plasma testosterone levels at first sampling were subdivided into groups, with a concentration interval of 5 nmol/L from 5 to more than 25 nmol/L, multifactor analysis of variance showed no significant difference between the values within the same group at each sampling, whereas at each sampling the groups remained highly significantly (P < 0.001) different from each other. The same applies to DHT levels when subdivided into groups with a concentration interval of 0.5 nmol/L. It is concluded that in healthy middle-aged and elderly men, single point plasma androgen measurements reflect fairly reliably the annual mean androgen level.