Dr. A. Tsujimura and his associates at Osaka University, Japan, discuss in the December 2003 issue of the Journal of Urology their approach to use of bioavailable testosterone (BT) in management of PADAM in 130 patients.

They first review the necessary measurements that must be done to calculate BT and FT: serum albumen (SA) which binds testosterone weakly as TA, serum sex hormone binding globulin (SHBG) which binds testosterone firmly as TSHBG and total testosterone (TT). Hence, TA+TSHBG+FT equals total testosterone (TT). TT and FT were assayed also separately. The equation used often to calculate free testosterone (cFT) and BT exists at www.issam.ch and requires input of SA, SHBG and TT. BT represents FT plus TA.

They also note that direct measurement of FT comes from two types of assay, one by analogue ligand immunoassay (aFT) that is easier than the other performed by equilibrium dialysis (dFT). Although the values for the former assay result in lower FT levels than the latter, they continue to use aFT preferentially because it correlates well with BT.

In addition to the above elements, they also measured luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

Multiple correlations resulted from their studies. Most importantly, in patients aged from 20 - 80 years, they found no significant decrease of TT, significant increase of SHBG, and significant decrease of BT and FT. BT correlated significantly with FSH, but not with LH. Higher (and better) IIEF-5 scores correlated with increased BT, but depression scores did not correlate well with BT.

SHBG concentrations in their study increased with age, and SHBG is reported to bind testosterone more strongly with aging. They surmise, therefore, that much of the decrease of BT and FT seen with aging is related to this change rather than to an absolute decrease in TT.

So, in conclusion, they confirm that BT continues to be useful in diagnosis and treatment of PADAM. They also point out that FT may find usefulness instead of BT, since FT values in this study correlated strongly with BT (r = 4.163, p < 0.0001). Their suggestion arises from the fact that determination of BT is more costly than aFT and "not covered by Japanese national health insurance." They caution, however, that multiple other causes for erectile dysfunction such as vascular disease, diabetes mellitus, and etc. must be considered along with endocrinologic deficiencies.

J Urol 2003;170,2345-2347