Testosterone Total(TT)

Testosterone follows a strong circadian rhythm in men. Peak values occur between 6 and 10 AM and trough values 12 hours later, with afternoon draws reading 20 to 30 percent lower than morning draws in the same patient. Acute illness, recent intense exercise, poor sleep, alcohol consumption, and short-term caloric restriction all transiently suppress the morning value by 10 to 25 percent. The Endocrine Society recommends confirming any abnormal value with a second early-morning draw on a separate day before initiating therapy. US laboratory reference ranges typically run from roughly 280 to 1,100 ng/dL, although this varies. Reference ranges are population-derived, not optimization-derived: a 60-year-old with a testosterone of 320 ng/dL falls "within reference range" but sits roughly two standard deviations below the average healthy 30-year-old. For longevity- and performance-focused men, target values in the upper half of the age-matched reference range (roughly 600 to 900 ng/dL in men aged 30 to 50) are commonly used as optimization rather than treatment thresholds. Most laboratories measure total T by immunoassay, which is accurate at the population level but can vary 15 to 20 percent at the individual level. LC-MS/MS is the reference method and is worth requesting whenever a result is borderline or therapeutic decisions are about to be made.