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Background Urinary 18-hydroxycortisol has been investigated as a marker of aldosterone-producing adenoma (APA). The aim of this study was to develop and validate a method for the measurement of 18-hydroxycortisol using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Methods Urine was collected over a 24-hour period in patients with APA ( n = 11), idiopathic hyperaldosteronism (IHA, n = 9), and essential hypertension (EH, n = 6). 18-Hydroxycortisol was extracted in solid-phase, and measured by LC-MS/MS based on selected reaction monitoring. Results The method allowed quantification of 18-hydroxycortisol with a lower quantification limit of 0.26 nmol/L, intra- and inter-assay coefficients of variation of Conclusions The proposed method met the basic analytical requirements and was considered to be useful in the screening and differential diagnosis of APA.

SUMMARY We report a newly diagnosed family in which a father and his two sons were found to be hypertensive and to have the rare familial condition dexametha-sone-suppressible hyperaldosteronism (DSH). All three patients became normotensive on dexamethasone treatment alone and have been successfully maintained on low doses of the drug for 6 months since diagnosis. Each of the patients had extremely high plasma and urinary concentrations of the recently discovered steroid 18-hydroxycortisol, which were more than ten times higher than the upper normal limit. Plasma levels were readily suppressed by dexamethasone treatment. The hypothesis that 18-hydroxycortisol might derive from 18-hydroxylation of recirculating Cortisol was tested by measuring plasma 18-hydroxycortisol levels during low-dose and high-dose hydrocortisone infusions, in a normal subject and in one of the patients with DSH. During the high-dose infusions (with plasma Cortisol levels of 3000-5000 nmol/1) there was net production of 18-hydroxycortisol within 8 h, but this was not observed during the low-dose infusions (plasma Cortisol levels 300-400 nmol/1). The origin of 18-hydroxycortisol remains uncertain: these findings do not support the recirculation theory, but lend weight to the alternative hypothesis that 18-hydroxycortisol is produced in transitional adrenocortical tissue. This steroid is of considerable value in the differential diagnosis of primary hyperaldosteronism and may also be important as a marker of transitional adrenal cell function.