SAT-161 Men With Borderline Low Serum Total Testosterone Concentration And Low Sexual Desire: Does The Calculation Of Free Testosterone Add Value?

Abstract Disclosure: G.A. Wittert: Sanofi, Besins, Amgen Inc. A. Vincent: None. M.M. Umapathysivam: None. D.R. Jesudason: None. S. Tafari: None. W. Goai: None. Background: Guidelines recommend the diagnosis of androgen deficiency by symptoms and low serum total testosterone concentration (TT). Studies vary as to whether the calculation of free testosterone (cFT) adds diagnostic accuracy when TT is borderline low. Aim: To determine whether cFT provides discriminant ability to infer that insufficient testosterone exposure is causally related to low sexual desire (SD) in men with borderline low TT.Methods: Cross-sectional analysis of a cohort of community-dwelling men (n=1195) aged 35 years and over with TT (LCMS), cFT (Vermeulen equation) and assessment of SD (dyadic scale of the Sexual Desire Inventory (SDI-D)). Borderline low TT and low cFT were defined as 6.1-12nmol/L and <0.2pmol/L respectively, and low SDI <19. Data were analysed by linear regression with and without adjustment for age and fat mass. Exact binomial confidence intervals for positive and negative predictive values (PPV and NPV), and false positive (FP) and negative (FN) estimates were generated. Results: There were 1169 men in the analysis sample (missing TT N=9, and SDI N=11). Mean age 55 years (SD 11.6); BMI 28.6kg/m2 (4.5); TT 17.3nmol/L (6.7); cFT 0.36pmol/L (0.15); SDI-D 34.3 (14.2). TT was borderline low in 207 men and low in 12 men. Men with TT<12nmol/L were older (p=0.02), more obese (p<0.001), with lower SDI scores (p<0.001) compared to men with TT ≥12nmol/L. In men with borderline low TT, a linear association between SDI-D score and cFT was explained by age and fat mass. The prevalence of low SDI was 23.3% (43/207) in men with borderline low TT, 41.9% in men with low cFT and 18.3% in men with normal/high cFT. (PPV = 41.9%, 95%CI=[27.0, 57.9]; NPV=81.7% [74.9, 87.3]; FP=58.1% [42.1, 73.0] & FN = 18.3% [12.7, 25.1]). Conclusion: Borderline low TT is associated with older age, greater adiposity and reduced sexual desire. While a cFT cut-off <0.20pmol/L helps rule out low sexual desire (NPV ≈ 82%), its false-positive rate and confounding by age and fat mass limit clinical applicability. Presentation: Saturday, July 12, 2025