Cortisol

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:

Method dependent.

200-650 nmol/L (morning peak).

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

Trough level (2000 h) 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 test-long and Synacthen 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.