Optimal Timing for Testosterone Level Testing
Testosterone levels should be drawn in the early morning (before 11 AM) for all men, with both measurements taken on separate days at the same time of day. 1
Standard Recommendation for Diagnostic Testing
The American Urological Association strongly recommends that both total testosterone measurements be conducted in an early morning fashion on separate occasions to establish a diagnosis of testosterone deficiency. 1
Morning sampling (before 11 AM) is necessary to capture peak testosterone levels and account for the circadian rhythm of testosterone production. 2, 3
Both measurements should be obtained using the same laboratory with the same method/instrumentation for consistency. 1
Age-Related Considerations
While some research suggests the circadian rhythm becomes blunted with age, the guideline evidence does not support relaxing the morning draw requirement based on age alone:
The AUA guideline makes no age-based exceptions to the early morning draw requirement. 1
Research data show that men younger than 45 years demonstrate clinically significant decreases in testosterone throughout the day (mean difference 149-207 ng/dL between early and late morning), requiring draws as close to 7 AM as possible. 4
For men 45 years and older, some research suggests draws before 2 PM may be acceptable, as total testosterone levels show less variation. 4, 5, 6
However, free testosterone and bioavailable testosterone still show significant variation with draw time even in older men (except those ≥75 years), making early morning draws preferable when measuring these parameters. 5
Critical Implementation Details
Free testosterone measurement by equilibrium dialysis should also be obtained in the morning when total testosterone is in the "grey zone" (230-350 ng/dL or 8-12 nmol/L). 1, 2
Morning draws are particularly important in obese patients or those with altered SHBG levels, where free testosterone measurement is essential. 2
Common Pitfalls to Avoid
Failing to obtain morning samples when testosterone levels are highest is a major diagnostic error that can lead to false-negative results. 2
Not repeating testosterone measurements on separate days to confirm low levels. 2
Drawing samples at inconsistent times of day between the two required measurements, which introduces unnecessary variability. 1