(372) Does Age Predict the Difference in Morning vs Afternoon Testosterone Levels?

Abstract

Abstract Introduction It is recommended that serum testosterone (T) level measurement be conducted in the early morning (AM) as T levels decrease in the afternoon (PM) due to the circadian rhythm in T secretion. This rhythm is reported to be blunted in older men. Objective This study aimed to define the magnitude and direction of the changes between morning and afternoon T levels across age groups. Methods The study population included men who had both AM (before 10 am) and PM (after 2 pm) total T (TT) levels within 3 months of each other. All TT measurements were performed using LCMS. We excluded patients with a prior orchiectomy, with T levels 1000 ng/dL, those with a history of androgen deprivation therapy, and patients on T therapy. Differences in AM and PM TT levels were quantified and stratified by age continuously. We reported the directionality of the changes based on increases or the decreases in T levels between AM vs PM. No difference was defined as a delta T levels between -100 to + 100 ng/dL, changes increasing or decreasing as >100 ng/dL. Correlation of TT difference between AM vs PM levels and age was calculated. Results 506 men were analyzed. Mean age = 63 ± 12 years. Mean of AM and PM TT levels were 425 ± 164 ng/dL and 397 ± 155 ng/dL, respectively (p < 0.001). While 63% of men had no significant difference (-100 to +100) between AM and PM levels, 24% had a > 100 ng/dl decrease, 13% > 100 ng/dl increase. Overall, 13% had higher PM and 24% lower PM TT levels. Neither AM nor PM TT levels were significantly associated with age. Age was weakly negatively correlated with the change between AM and PM levels (r = 0.10, p = 0.03). That is, the mean difference between AM and PM levels was more pronounced for lower ages and approached zero as age increased. Conclusions While age was not associated with mean AM or PM total T levels, this study did find differences in the magnitude of the difference by age. Disclosure No