Glucose values obtained during an oral glucose toler- ance test tend to be higher when the test is performed in the afternoon than when the test is performed in the morning. The cortisol rhythm apparently may be responsible for the discrepancy noted in the results of an oral glucose tolerance test performed in the afternoon.2
Thyrotropin levels peak during the late evening hours, with the lowest values observed around midday.20,21 Growth hormone levels during waking hours are minimal, with increases noted during sleep.1
Reproductive hormones, such as luteinizing hormone, follicle-stimulating hormone, and testosterone, are released in bursts lasting barely 2 minutes, making accurate assess- ment of their concentration problematic.8