What does it measure?
Cortisol is made by the adrenal glands and helps regulate metabolism and the response to stress. It usually rises toward waking and falls later in the day. A PM blood sample captures one point in that rhythm, rather than measuring your everyday stress level.
Before the test
- Timing
- Attend at the requested afternoon or evening time and record the exact collection time.
- Context
- Mention recent stress, exercise, sleep pattern, and steroid medicines, including creams and inhalers.
What can the result mean?
A result that looks low against a morning interval may be expected later in the day. A higher PM value can have several explanations, including altered timing, illness, or a hormone disorder. A single result cannot diagnose Cushing syndrome, adrenal insufficiency, or “adrenal fatigue.” [1]
When is it useful, and how is it read?
Read it only within the reason for an adrenal assessment and the exact collection time. If an endocrine disorder is suspected, the clinician chooses the appropriate timed or dynamic testing; an AM-to-PM comparison alone is not a diagnosis. [1]
What can affect it?
Exact collection time, sleep schedule, shift work, acute stress, pregnancy, and steroid medicines matter. Steroids include inhalers, creams, and injections as well as tablets; do not stop prescribed treatment without advice. [1]
Myth: «Afternoon cortisol is a simple stress score»
Cortisol follows a daily rhythm and changes with illness and many medicines. One afternoon blood result cannot measure the amount of everyday stress you are carrying. [1]
Questions you might have
Can I use the morning reference range for a PM sample?
No. Cortisol changes through the day, so the collection time belongs with the result. [1]
Does one evening reading diagnose an adrenal disorder?
No. The clinician may need a different timed test or other testing chosen for the suspected condition. [1]
What comes next?
Your clinician may choose morning cortisol, timed saliva or urine testing, or a stimulation or suppression test depending on the question. Match the test to the concern before drawing conclusions. [1]
Was this interpreted with the correct collection time and sleep pattern, and is a different cortisol test more appropriate?
The reference interval and units on your report are part of understanding your result. Understand units, reference intervals, and treatment targets.
Sources & references
Medical references & original research
Books we consulted
References that informed our explanations of the test and its context.
- Pagana KD, Pagana TJ, Pagana TN. Mosby’s Diagnostic and Laboratory Test Reference. 14th ed. Elsevier; 2019.
Practical-section sources accessed: .
For general health education. Interpreting your result and deciding on tests or treatment requires your health context and a qualified clinician.
