Cortisol Normal Range
May 24, 2022
Source: Cainiu Health
Dr. Pan Yongyuan
Introduction
The normal range for serum cortisol at 8 a.m. is 50–230 μg/L. Morning cortisol levels represent the peak concentration of the day and are used to assess adrenal cortical function. The normal range for serum cortisol at 4 p.m. is 30–160 μg/L. Cortisol levels in the afternoon decline from morning values but remain at a significant concentration.
The normal range of cortisol varies depending on the time of measurement: serum cortisol levels at 8 a.m. may be 50–230 μg/L, at 4 p.m. 30–160 μg/L, and at midnight <80 μg/L. The analysis is as follows:
Serum cortisol levels at 8 a.m. normally range from 50 to 230 μg/L. Morning cortisol represents the daily peak and is used to assess adrenal cortical function. At 4 p.m., the normal serum cortisol range is 30–160 μg/L. Cortisol levels in the afternoon decline from morning values but remain at a relatively stable concentration. By midnight, cortisol should be less than half the 4 p.m. level—i.e., <80 μg/L under normal conditions. Midnight cortisol represents the daily nadir and is used to evaluate the circadian rhythmicity of the adrenal cortex.
Cortisol secretion follows a distinct circadian rhythm, peaking in the early morning, gradually declining throughout the day, and reaching its lowest point at night. Therefore, when interpreting cortisol levels, the timing of sample collection must be taken into account, as it significantly influences results. Different assay methods may yield varying cortisol measurements; thus, when comparing cortisol values across laboratories, differences in analytical methodology should be carefully considered.
