Determination of cortisol and associated glucocorticoids in serum and urine by an automated liquid chromatographic assay.

We describe a method for the determination of urinary free cortisol and glucocorticoids in plasma, used in the diagnosis of adrenal disorders, based on automated reverse-phase high-performance liquid chromatography (HPLC). The within-day and day-to-day CVs were less than 5.5 and 8.0%, respectively. The calibration curves for cortisol and 11-deoxycortisol were linear up to 2000 nmol/L. Cortisol concentrations as low as 3.5 nmol/L in 1 mL of plasma or urine can be measured. Correlation of HPLC results for 40 plasma specimens with those by radioimmunoassay showed r = 0.965. This method is sensitive and free from the interference habitually encountered in immunoassays, and can thus be proposed for research and as a potential reference method.