[Variations in the concentration of the sex hormone binding globulin is a major factor causing a variation in total testosterone values]. / Variaciones en las concentraciones de globulina transportadora de hormonas sexuales como causa importante de alteraciones en las concentraciones de testosterona total.

Measurement of total testosterone concentrations is the initial test for the diagnosis of androgen deficiency or excess in men. However, total testosterone concentrations may be affected by alterations in sex hormone binding globulin (SHBG) concentrations. Most circulating testosterone is bound to SHBG and to albumin and only 0.5-3% of circulating testosterone is unbound or free. The free fraction can be measured by equilibrium dialysis or calculated using published algorithms. The term bioavailable testosterone refers to unbound testosterone plus albumin-bound testosterone; this term reflects the view that, in addition to unbound testosterone, albumin-bound testosterone is readily dissociable and thus bioavailable. Bioavailable testosterone can be measured by precipitation methods or calculated from total testosterone, SHBG, albumin concentrations and their affinity constants. Free testosterone measurements by analog methods are frequently available, but these measurements are affected by alterations in SHBG and are inaccurate. We report the cases of a 42-year-old man with testosterone excess and a 29-year-old man with testosterone deficiency, in whom total testosterone concentrations were affected by SHBG alterations.

Variaciones en las concentraciones de globulina transportadora de hormonas sexuales como causa importante de alteraciones en las concentraciones de testosterona total / Variations in the concentration of sex hormone binding globulin (SHBG) is a major factor causing variations in total testosterone values

La determinación de testosterona total es el primer paso para establecer el diagnóstico de déficit o de exceso de testosterona en varones, pero las concentraciones de testosterona total pueden verse afectadas por un exceso o un déficit de globulina transportadora de hormonas sexuales (SHBG). La mayor parte de la testosterona total circulante se encuentra unida a SHBG y albúmina y sólo el 0,5-3% de la testosterona circulante es testosterona libre. La testosterona libre se puede medir por diálisis en equilibrio o calcularla mediante algoritmos publicados. La testosterona biodisponible hace referencia a la testosterona no unida a proteínas más la testosterona unida a la albúmina; el término biodisponible refleja el hecho de que la testosterona unida a la albúmina es fácilmente disociable. La testosterona biodisponible se puede evaluar por el método de precipitado de SHBG o aproximarnos a su concentración mediante cálculos que utilizan las concentraciones de testosterona total, SHBG, albúmina y sus constantes de afinidad. Debemos tener en cuenta que hay ensayos para determinar testosterona libre que pueden verse afectados por las alteraciones de la SHBG y, por lo tanto, son inadecuados. Presentamos el caso de un varón de 42 años con exceso de testosterona y el de un varón de 29 años con déficit de testosterona, que se debían a la influencia de la testosterona total por la SHBG (AU)

Measurement of total testosterone concentrations is the initial test for the diagnosis of androgen deficiency or excess in men. However, total testosterone concentrations may be affected by alterations in sex hormone binding globulin (SHBG) concentrations. Most circulating testosterone is bound to SHBG and to albumin and only 0.5-3% of circulating testosterone is unbound or free. The free fraction can be measured by equilibrium dialysis or calculated using published algorithms. The term bioavailable testosterone refers to unbound testosterone plus albumin-bound testosterone; this term reflects the view that, in addition to unbound testosterone, albumin-bound testosterone is readily dissociable and thus bioavailable. Bioavailable testosterone can be measured by precipitation methods or calculated from total testosterone, SHBG, albumin concentrations and their affinity constants. Free testosterone measurements by analog methods are frequently available, but these measurements are affected by alterations in SHBG and are inaccurate. We report the cases of a 42-year-old man with testosterone excess and a 29-year-old man with testosterone deficiency, in whom total testosterone concentrations were affected by SHBG alterations (AU)