skip to main content

Cortisol Circadian Peak — FRCA Primary MCQ

Instant feedback + full explanation. One question, done properly.

HardPhysiology - Endocrine & MetabolicCortisol Circadian PeakFRCA Primary

An outpatient is investigated for possible adrenal insufficiency using a single serum cortisol concentration. She works daytime hours and has slept normally. At which sampling time is a low value most informative before dynamic testing?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: A — Around 08:00, near the expected diurnal peak

The best answer is “Around 08:00, near the expected diurnal peak”. In a person with a normal daytime schedule, cortisol normally rises before waking and is highest in the early morning; a low approximately 08:00 value is therefore more concerning than an evening value and may prompt dynamic testing. Cortisol is pulsatile and illness, shift work and exogenous steroids alter interpretation. The other options misstate the usual diurnal pattern.

Reference: RCoA, Primary FRCA syllabus: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf; Circadian regulation of brain and behavior: a neuroendocrine perspective: https://pmc.ncbi.nlm.nih.gov/articles/PMC7594017/