How should a cortisol sample be collected for accurate measurement?

• A. Once in the morning
• B. Twice (morning and afternoon)
• C. Three times daily
• D. Random sampling

Answer: (B)

Cortisol has a clear daily rhythm: it peaks after awakening and then gradually declines through the day. A single measurement captures only a moment in that cycle and can be thrown off by recent stress, sleep disruption, illness, or the exact time of collection. By taking two samples—one in the morning and one in the afternoon—you obtain a picture of how the level rises and then falls, which makes it possible to assess the overall pattern of cortisol production more reliably. This approach reduces misinterpretation that can come from a lone value and gives a better view of adrenal function. Avoid relying on random sampling or multiple unrelated times, as they don’t align with the natural diurnal pattern and are less informative. Ensure the draws are timed consistently relative to waking and handled properly to avoid artifactual changes.