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.
Laboratoire Central de Biochimie, Hôpital de l'Antiquaille, Hospices Civils de Lyon, France.
H
H
Déchaud
H
H
Lejeune
M
M
Garoscio-Cholet
R
R
Mallein
M
M
Pugeat
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