High Prevalence of Low Serum Biologically Active Testosterone in Older Male Veterans.

OBJECTIVES: Assess the prevalence of hypogonadism in older male Veterans by comparing direct measurements of total testosterone (T) and bioavailable testosterone (BioT) versus indirect BioT values derived from existing and newly developed regression analyses.

DESIGN: Cohort study.

SETTING: Malcom Randall VA Medical Center, Gainesville, FL.

PARTICIPANTS: Community-dwelling male Veterans aged 60 and older (n = 203).

MEASUREMENTS: Total T, BioT, albumin, sex hormone-binding globulin (SHBG), and body mass index were evaluated. Blood values were assessed via liquid chromatography-tandem mass spectrometry (LC-MS/MS) and clinical or commercially available immunoassays to compare accuracy among assessment techniques. Existing and newly developed multiple regression analyses were evaluated to assess accuracy in predicting BioT.

RESULTS: Total T was 13.80 ± 6.25 nmol/L (398 ± 180 ng/dL) and was low (≤10.4 nmol/L or ≤300 ng/dL) in 34% of participants. SHBG was 58 ± 35 nmol/L and elevated (≥62 nmol/L) in 36% of participants. BioT was 1.94 ± 0.97 nmol/L (56 ± 28 ng/dL), with 72% of participants below the clinical cutoff (≤2.43 nmol/L or ≤70 ng/dL). Albumin was within the normal clinical range. Total T and BioT measured via immunoassay and LC-MS/MS were moderately to highly correlated, with no differences between assessment methods. Several existing predictive equations overestimated BioT by 74% to 166% within our cohort (P < .001). A newly developed regression model that included total T, SHBG, albumin, and age more accurately predicted BioT, with values correlated (r = 0.508, P < .001) and comparable to LC-MS/MS.

CONCLUSION: In our cohort, the prevalence of low total T was higher and low BioT was markedly higher than reported in the general age-matched population, indicating a greater incidence of hypogonadism in older male Veterans. In addition, existing empiric formulae, derived from other populations produced BioT values that were considerably greater than those directly measured, whereas our newly developed regression analysis provides improved predictive capabilities for older male Veterans.