Distribution of testosterone in plasma proteins during replacement therapy with testosterone enanthate in patients...

In five hypogonadal men treated with 250 mg of testosterone enanthate once every three weeks, total testosterone, "free" testosterone and the percent of testosterone bound to the sex hormone-binding globulin (SHBG) and albumin were determined during three weeks. Immediately after the injection total plasma testosterone rapidly increased about four times the starting level closely paralleled by the concentration of "free" testosterone. We found that if the concentration of SHBG had been reached albumin took over the surplus of the testosterone. Whereas in the first and second week after the injection, high and sufficient levels of testosterone were determined, both total and "free" testosterone approached the lower limit of the normal male range in the third week, i.d. 300 ng/dl, or 5 ng/dl, respectively. In one patient with hypalbuminemia, "free" testosterone decreased during the third week below 3 ng/dl though his total testosterone remained sufficient high. This patient complained about symptoms of androgen deficiency. We explained this with his impaired capacity to bind the excess of testosterone by albumin. We concluded that though the concentration of total testosterone may be sufficient high, "free" testosterone can decrease to very low levels due to disturbance in the distribution of the androgen between the plasma proteins.