Determination of bioavailable testosterone [non sex hormone binding globulin (SHBG)-bound testosterone] in a population of healthy French men: influence of androstenediol on testosterone binding to SHBG.
BACKGROUND
Bioavailable testosterone (BT) is measured [assayed BT (aBT)] or calculated (cBT) in the diagnosis of hypogonadism in men. The cBT depends, however, on the values of the association constants of total testosterone (TT) for sex hormone-binding globulin (SHBG; K(s)) and albumin (K(a)), and its use therefore remains controversial.


METHODS
In 503 selected, untreated healthy men, 20-74 years old, we measured TT, dihydrotestosterone (DHT), and androstenediol (5-diol) by GC-MS, SHBG by RIA, and BT after ammonium sulfate precipitation or by calculation according to the law of mass action.


RESULTS
A slight decrease in TT, significant decreases in BT and 5-diol, no variation in DHT, and an increase in SHBG were observed with age. In young males (< or = 39 years), the lower normal limits were between 2.30 and 2.72 nmol/L for aBT and 8.50 nmol/L for TT. For K(s) = 1 x 10(9) L/mol and K(a) = 3.6 x 10(4) L/mol, the lower cBT limit was found to be 2-fold higher than for aBT. With optimized K(s) = 1.9 x 10(9) L/mol and K(a) = 2.45 x 10(4) L/mol, cBT values close to aBT were obtained. When 5-diol was included in the model as a competitive SHBG inhibitor, the correlation between cBT and aBT was better and the cBT:aBT ratios vs 5-diol were less biased.


CONCLUSIONS
Lower normal serum aBT concentration in normal men appears to be between 2.30 and 2.72 nmol/L. Much higher serum cBT concentrations are associated with use of different association constants that may be inappropriate. When using the optimized binding constants, taking age-related 5-diol values into consideration slightly improves prediction of cBT.
Giton
Frank
F
Assistance Publique-Hôpitaux de Paris (AP-HP), Biological Center of Investigations, University Hospital Group, Sud Henri Mondor, Faculté de Médecine, Créteil, France. giton@univ-paris12.fr
Urien
Saïk
S
Born
Catherine
C
Tichet
Jean
J
Guéchot
Jérôme
J
Callebert
Jacques
J
Bronsard
Françoise
F
Raynaud
Jean Pierre
JP
Fiet
Jean
J
D000328:Adult; D000367:Age Factors; D000368:Aged; D000645:Ammonium Sulfate; D015114:Androstenediol / Q000097:blood*; D011232:Chemical Precipitation; D013196:Dihydrotestosterone / Q000097:blood; D005602:France; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D008297:Male; D008875:Middle Aged; D011485:Protein Binding; D011863:Radioimmunoassay; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism*; D013739:Testosterone / Q000097:blood*
D012738:Sex Hormone-Binding Globulin; D013196:Dihydrotestosterone; D013739:Testosterone; D015114:Androstenediol; D000645:Ammonium Sulfate