Primary aldosteronism (PAL) is gaining recognition as an important cause of hypertension, and attention is focusing more critically on the reliability of screening tests for PAL. However, less attention has focused on reliable tests to establish a firm diagnosis, or on tests to differentiate the surgically correctable form, unilateral aldosterone-producing adenoma (APA), associated with a ‘normal’contralateral adrenal, from other forms.

In this issue of the journal, Ferrari et al.[1] make a small but significant contribution to these difficult but important questions by showing that immunoreactive renin (irR) can probably be substituted for the theoretically more variable (ie because of widely differing conditions of assay) plasma renin activity (PRA), which incorporates assessment of renin substrate (angiotensinogen), and which has contributed so much to our early understanding of renin–angiotensin–aldosterone physiology. More reproducible assays are essential at this critical time for the management of PAL because, due to the wide availability of commercial ‘kits’, the measurement of aldosterone to renin ratio (ARR) has moved from the basic research or Specialized Unit laboratory, with meticulous quality control, clinical feedback and long experience, to the busy shrinking budget-driven general hospital laboratory and to the profit-driven private laboratory. Although clearly preferable, the smaller laboratories possibly could not cope with the heavy load of widely based screening. It might reasonably be expected that there is less laboratory to laboratory variability with irR (with an international standard for renin) than with PRA, permitting comparison and even pooling of results in patients from different clinical units. This might strengthen our combined ability to resolve some of the important issues regarding screening for PAL, together with its firm diagnosis and optimal treatment.