Radioimmunoassay of testosterone not bound to sex-steroid-binding protein in plasma.
To measure the concentration of testosterone (T) that is not bound to sex-steroid-binding protein (SBP) in plasma, we quantified by radioimmunoassay the T in the supernates of plasma samples after precipitation with 50%-saturated ammonium sulfate. The concentrations of non-SBP-bound T. directly measured with this assay, correlated significantly (P less than 0.001) with those deduced from measurement of the percentage of non-SBP-bound T determined with [3H]T as tracer or from mathematical models according to the law of mass action. It also correlated significantly with the ratio of T to SBP and with the concentration of nonbound T. As determined with this assay, the mean concentration of non-SBP-bound T in normal men was higher in young (4.67, SD 2.68 nmol/L; n = 30) than in older (greater than 40 years) subjects (2.48, SD 1.61 nmol/L; n = 35; P less than 0.001) and lower than normal in hyperthyroid (1.61, SD 0.91 nmol/L; P less than 0.01) or infertile men (3.28, SD 1.70 nmol/L; P less than 0.01). In women, non-SBP-bound T was higher in hirsute patients (0.24, SD 0.11 nmol/L; P less than 0.01) and was lower during pregnancy (0.09, SD 0.05 nmol/L; P less than 0.05) than in normal women during the follicular phase (0.16, SD 0.07 nmol/L). We conclude that this direct measurement of non-SBP-bound T in plasma is suitable for routine use and represents a reliable index of androgenicity in human pathology, particularly when alterations of the binding capacity of SBP modify the concentrations of total T.
Déchaud
H
H
Laboratoire Central de Biochimie, Hôpital de l'Antiquaille, Hospices Civils de Lyon, France.
Lejeune
H
H
Garoscio-Cholet
M
M
Mallein
R
R
Pugeat
M
M
D000328:Adult; D000368:Aged; D000375:Aging / Q000097:blood; D004958:Estradiol / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011247:Pregnancy; D011863:Radioimmunoassay / Q000379:methods; D012737:Sex Factors; D013739:Testosterone / Q000097:blood* / Q000378:metabolism
D013739:Testosterone; D004958:Estradiol