Endocrine Abstracts

Urine 18-hydroxy cortisol ('18OHF') measurements are claimed to have the potential to discriminate between primary hyperaldosteronism due to either Conn's syndrome/adrenal adenoma (increased values) or idiopathic adrenal hyperplasia (normal values), and also to identify cases of glucocorticoid-suppressible hyperaldosteronism ('GSH').
We have evaluated three urine 18-OHF methods using a panel of samples from patients with primary hyperaldosteronism [due to either adenoma (N=6) or hyperplasia (N=6)], GSH (N=9), or essential hypertension (N=38). Diagnoses were defined by genotype for GSH, surgical cure for adenoma, and lack of low renin/high aldosterone for essential hypertension. Samples were analysed without knowledge of the diagnosis. The methods used were 'in-house' radioimmunoassay (RIA), 'in-house' time-resolved fluorometric assay (DELFIA ) and gas chromatography mass spectrometry (GC-MS) performed in the Edinburgh, Southampton and Glasgow laboratories respectively. Upper limits of normal were 606, 550 and 385 nmol/24 hrs for the RIA, DELFIA and GC-MS assays respectively.
Overall, results for the three assays showed good correlation, but there were large bias differences: RIA bias was greater than DELFIA which was greater than GC-MS.
Discrimination between adenoma and hyperplasia patients was best for the DELFIA method, with no overlap between results for these two groups. The RIA, DELFIA and GC-MS assays gave increased results in 6/6, 6/6 and 2/6 patients respectively in the Conn's adenoma group.
All three methods gave significantly elevated results for the GSH group compared with the idiopathic hyperplasia and essential hypertension groups. High results were obtained in 9/9, 8/9 and 7/9 patients with GSH and 6/47, 0/47 and 2/47 patients with idiopathic hyperplasia or essential hypertension for RIA, DELFIA and GC-MS methods respectively
We conclude that the clinical diagnostic value of urinary 18-OHF measurements is method-dependent. At present we are investigating why the DELFIA assay gave improved discrimination between Conn's adenoma and idiopathic hyperplasia compared to the GC-MS method. However, with appropriate methodology, 18OHF remains a useful measurement in the differential diagnosis of primary hyperaldosteronism.