Sex Steroids and Androgen Biomarkers in the Healthy Man Study: Within-Person Variability and Impact of Fasting.

OBJECTIVE: Serum testosterone measurements in clinical practice mostly utilize "direct" (non-extraction) immunoassays which have method-specific bias due to steroid cross-reactivity and non-specific matrix artefacts. Although more accurate, sensitive, and specific liquid chromatography-mass spectrometry (LCMS) dominates in clinical research, the within-person variability of serum testosterone in healthy men using LCMS measurement is not reported.

DESIGN: Longitudinal multi-sampling observational study of men in excellent health over three months.

METHODS: Elite healthy men (n=325) over 40 years of age in excellent, asymptomatic health provided nine blood samples over 3 months with serum testosterone, dihydrotestosterone (DHT), estradiol (E2) and estrone (E1) measured by validated LCMS with conventional biochemical and anthropometric variables.

RESULTS: Quantitative estimates of within-person variability within day and between day, week, month, and quarter were stable other than an increase due to fasting. The androgen biomarkers most sensitive to age and testosterone among widely used biochemical and anthropometric variables in middle-aged and older men were identified.

CONCLUSIONS: This study provides estimates of variability in serum testosterone and the best androgen biomarkers that may prove useful for future studies of androgen action in male ageing.