Cortisol - plasma or serum

Last updated: Saturday, 27, March, 2004

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5 mL blood in lithium heparin, EDTA or plain tube.

Random assay or assessment of diurnal variation is rarely indicated.



Reference Interval

200-650 nmol/L (morning peak).

Higher levels may be seen in stressed patients and in those on oral contraceptives.

Trough level (2000h) should be <50% of the morning peak.


Assessment of adrenocortical function as part of a suppression or stimulation test.

Random cortisol assay is only indicated as an initial test to exclude pituitary insufficiency or in the confirmation of Addisonian crisis.

See Dexamethasone suppression testSynacthen stimulation test and Insulin hypoglycaemia stimulation test.


See dynamic tests, as indicated above.


Pavord SR et al. Clin Endocrinol 1992; 36: 135-139.

Trainer PJ and Grossman A. Clin Endocrinol 1991; 34: 317-330.