Cortisol - plasma or serum

Last updated: Saturday, 27, March, 2004

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Item Process
Specimen

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

Random assay or assessment of diurnal variation is rarely indicated.

Method

Immunoassay.

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.

Application

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.

Interpretation

See dynamic tests, as indicated above.

Reference

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

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