Estradiol biodisponible (non-SHBG-bound E2). Dosage ou calcul en relation avec la densité minérale osseuse lombaire (L1-L4) chez l'homme âgé

With age, decreased levels of bioavailable T and E1 + E2 are mainly the result of the increase of SHBG levels. Several studies have shown the association of low levels < 11 pg/ml (40 pM) of bioavailable estradiol with vertebral fractures and osteoporosis in older men. They used assayed E2 Bio or calculated non-SHBG-bound E2 calculated using the equation derived from the law of mass action for the model: two binding proteins (SHBG, Albumin) and two ligands (T, E2) (FE2cII Södergard) while serum SHBG, albumin, T and E2 are determined experimentally in every sample. The aim of the study is to evaluate the performance of E2 Bio and FE2cII associated with vertebral osteoporosis on 62 men (median age: 64 years). As expected, SHBG increases markedly with age (P = 0.003) and Ttot increases with SHBG (P = 0.0003). DMO and T score are positively correlated (P = 0.086-0.048) with E2 Bio in men with E2 Bio < 40 pM and are not correlated (P = 0.70-0.48) in men with E2 Bio > 40 pM. E2 Bio (P < 0.003) is inversely associated with SHBG levels but FE2cII is not correlated with SHBG (P > 0.45) and with DMO or T score adjusted for body weight (P = 0.48). Considering the lack of sensitivity of calculated FE2cII to estimate the "non-SHBG-bound E2", the bioavailable estradiol assay by ammonium sulfate precipitation is the preferred method for detecting elderly men in the lowest quartile for E2 Bio and at risk for developing osteoporosis later in life.