Monoclonal antibodies specific for 18-hydroxycortisol and their use in an enzyme immunoassay for human urinary 18-hydroxycortisol for diagnosis of primary aldosteronism.

We report the development of a monoclonal antibody-based enzyme immunoassay (EIA) specific for human urinary 18-hydroxycortisol, a biological marker of primary aldosteronism. Hybrid cell lines (hybridomas) were isolated after fusion between myeloma cells and spleen cells prepared from mice immunized with 18-hydroxycortisol conjugate. A competitive EIA suitable for the measurement of urinary 18-hydroxycortisol was developed using the mouse monoclonal antibody, KTM-41, which showed no practical cross-reaction with related endogenous steroids and synthetic steroids. This EIA meets all the requirements of routine clinical assay in terms of sensitivity (detection limit: 20 nmol/L), reproducibility (total CV: 8-15%), accuracy (recovery: 88-115%), simplicity and rapidity (< 3 h). Urinary 18-hydroxycortisol measured by the present assay was 153 +/- 119 nmol/L (mean +/- SD, range, 28-485) and 1787 +/- 1180 (range, 810-4264) in normal subjects (n = 20) and in patients with primary aldosteronism (n = 7), respectively. Clinical validation of the assay was confirmed by an appropriate decrease in urinary 18-hydroxycortisol level in patients with primary aldosteronism subsequent to adrenalectomy: 171 +/- 141 nmol/L (range, 41-466).