Testostérone libre ou biodisponible : dosages ou calculs. Comparaison critique de différents modes d'approche |
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| Institution: | 1. Service de pneumologie, hôpital Clavary, BP 53149, 06135 Grasse cedex, France;2. Centre de soins de suite et de rééducation « La Maison du Mineur », 577, avenue Henri-Giraud, 06141 Vence, France;3. Service de gérontologie et de rhumatologie, hôpital Clavary, BP 53149, 06135 Grasse cedex, France;1. Institute for Myeloma and Bone Cancer Research, West Hollywood, CA;2. Comprehensive Blood and Cancer Center, Bakersfield, CA;3. Cancer Care Associates for Research and Excellence, Encinitas, CA;4. US Oncology Research and Cancer Care Centers of South Texas, San Antonio, TX;5. Horizon Oncology Center, Lafayette, IN;6. Cedars-Sinai Medical Center, Los Angeles, CA;7. The Oncology Institute of Hope and Innovation, Downey, CA;8. Center for Cancer and Blood Disorders, Bethesda, MD;9. Department of Hematology/Oncology, Weill Cornell Medical College, Clinical Research Alliance, New Hyde Park, NY;10. Robert A. Moss Medical Oncology and Hematology, Fountain Valley, CA;11. US Oncology Research and Rocky Mountain Cancer Centers, Denver, CO;12. Onyx Pharmaceuticals, Inc., an Amgen subsidiary, South San Francisco, CA;13. Sarah Cannon Research Institute, Nashville, TN;1. Cabinet de médecine sexuelle, 4, rue des États-Unis, Cannes, France;2. Centre hospitalier princesse Grâce, 98000 Monaco Monaco;3. Service de médecine de la reproduction, Hôpital Femme Mère Enfant, HCL, Bron, France;4. Cabinet d’Urologie, 265, avenue des États du Languedoc, Montpellier, France;5. Cabinet de Médecine sexuelle, 11, rue Magellan, 75008, Paris, France;6. Service d’oncologie, CHU de Martinique, Fort de France, France;7. Service d’Urologie, chirurgie de la transplantation, Hôpital Edouard Herriot, CHU de Lyon, France;8. Médecine de la Reproduction, CHU de Toulouse, site de Paule de Viguier, Toulouse, France;9. Département d’urologie, transplantation rénale et andrologie, Hôpital Rangueil, CHU de Toulouse, France;1. Service d’endocrinologie, hôpital Saint-Antoine, AP–HP, 184, rue du Faubourg-Saint-Antoine, 75012 Paris, France;2. Sorbonne universités, université Pierre-et-Marie-Curie–Paris 6, 75012 Paris, France;3. Inserm U933, 75012 Paris, France |
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| Abstract: | The aim of the study is to find the most reliable practical approach to the estimation of free or bioavailable serum testosterone. We compare assayed values of bioavailable testosterone (T Bio), Free testosterone DPC (Free T DPC), total testosterone (Ttot) and calculated Free Androgen Index FAI = Ttot/SHBG] × 100, calculated Free Testosterone using the equation derived from the law of mass action for the model: two binding proteins (SHBG, Albumin) and two ligands (T,E2) (FTcII Södergaard) or one ligand (T) (FtcI Kaufman and Fiers). Serum SHBG, Albumin, E2 are determined exprimentally in every sample. The bioavailable (or non-SHBG bound) T correlates well with Free T by ultrafiltration (r = 0.96; P < 0.01), is easy to perform, reliable and sensitive if a particular care is ensured in the purification of the tracer. Assayed women values of T Bio agreed well with calculated values for FTc II or FTc I (r = 0.93; P < 0.01) using the laws of mass action. In contrast, the ratios of FTc II/T Bio and FTc I/T Bio (which should be constant if indexes reflect T Bio) remain negatively SHBG dependent for women and positively SHBG dependent for men confirming that the assumptions of the model are too simplified and the association constants Ka values too approximative. Calculated FTc is an acceptable substitute for an estimation of bioavailable T if we presume women with standard SHBG binding conditions and sera free of significant amounts of substances or steroids that could occupy the binding sites in the SHBG moiety and invalidate the calculation. Although showing a good correlation (r = 0.89; P < 0.01) with T Bio, FAI is not a useful index: the FAI/T Bio ratio is negatively correlated (r = –0.86 P < 0.001) with SHBG and overestimate strongly the SHBG binding capacity contribution for a reliable quantification of the non-SHBG bound T. The Free T DPC is inaccurate, not sufficiently sensitive, not free of proteins effects and less correlated with T Bio (r = 0.49; P < 0.05) than Ttot (r = 0.64; P < 0.01) for women! |
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