24-hour urine cortisol: purpose and collection

It is used when a clinician needs information about overall cortisol production rather than the level at one moment. Interpretation requires the laboratory range and relevant clinical details.

Cortisol is made by the adrenal glands and helps regulate metabolism, blood pressure and the response to physical stress. Its level changes naturally across the day, which is why collecting all urine over a timed period can be useful.

An unusually high or low measurement is not a stand-alone diagnosis. Acute illness, disrupted sleep, strenuous activity, collection errors and corticosteroid medicines can affect the assessment, and repeat or different tests may be needed.

Choose a day when you can collect every urination. At the starting time, pass urine into the toilet and write down that time; after this, place all urine into the supplied collection container for the next 24 hours.

At the finish time the following day, collect that final urination. Keep the container refrigerated or otherwise stored as the laboratory specifies, and return it according to the instructions.

Give the clinician a complete list of tablets, injections, creams, inhalers and supplements, especially anything containing a corticosteroid. Do not stop a prescribed steroid suddenly or alter the dose solely for this test unless the prescriber has given a plan.

The urine collection is non-invasive. Obtain urgent medical help for collapse, severe dizziness with fainting, confusion, repeated vomiting with inability to drink, or profound weakness, rather than waiting for a cortisol result.

Contact the requesting clinic if you become acutely unwell during collection or cannot take prescribed steroid medicine. Also report a missed sample or incorrect storage because these issues can make the result unreliable.

Discuss whether your sleep schedule, recent illness, exercise routine or medicines could influence the timing. Ask whether another cortisol test is planned and how the full set of results will guide the next step.