The clinical utility of two renin mass methods to detect primary hyperaldosteronism compared with renin activity.

BACKGROUND

Primary hyperaldosteronism (PHA) is characterized by a raised plasma aldosterone concentration (PAC) with suppressed plasma renin activity (PRA). We evaluated two renin mass methods for PHA detection compared with the PAC:PRA ratio.

METHODS

Samples from patients attending a specialist hypertensive clinic were analysed by Liaison automated chemiluminescent immunoassay and Diagnostic Systems Laboratories (DSL) immunoradiometric assay (IRMA) for renin mass; I(-125) radioimmunoassay of angiotensin I generated from endogenous angiotensinogen for PRA; Siemens Coat-a-count radioimmunoassay for PAC. Subjects included those on β-blockers which suppress renin, causing an equivalent biochemical picture to PHA. Aldosterone/renin ratios (ARR) were calculated for PRA, DSL and Liaison methods. The first 100 subjects were used to identify cut-off ratios ensuring maximum specificity at 100% sensitivity for PHA detection. This cut-off was retested in a subsequent population (n = 43).

RESULTS

A Liaison renin of 5 ng/L separated PRAs of ≤0.5 from ≥0.6 pmol/mL/h. The DSL method had greater scatter. In population 1 (18 PHA), cut-off ratios of >118 pmol/ng (Liaison) and >60 pmol/ng (DSL) gave specificities of 58.5% and 61%, respectively, with 100% sensitivity. If criteria for PHA included PAC ≥350 pmol/L and excluded β-blocked subjects, specificity increased to 95.1% and 90% for Liaison and DSL, respectively. In population 2 (6 PHA), specificities for Liaison and DSL ARRs were 86.4% and 78.3%. Using the ratio with PAC and β-blocker criteria, specificities for Liaison and DSL were 97.3% and 86.5%, respectively.

CONCLUSIONS

The Liaison ARR used with PAC and β-blocker criteria provided an automatable alternative to identify the same patients as the PAC:PRA ratio.