Aldosterone Assays: An Urgent Need for Improvement

It should not be forgotten that the concentration of aldosterone in plasma is only ∼1 thousandth that of cortisol. In this issue of Clinical Chemistry , Schirpenbach et al.(1) draw much-needed attention to current problems with measurement of aldosterone. The issue is extremely important in clinical practice after recognition that primary aldosteronism is a much more common cause of hypertension than previously thought(2)(3)(4)(5)(6). Consequently, we have seen a marked increase in screening for this disorder by measuring the ratio of aldosterone to renin (ARR) and by suppression testing to definitively confirm or exclude the diagnosis, both tests that critically depend on reliable aldosterone measurement. Because every hypertensive patient deserves testing to reliably diagnose or exclude this specifically treatable and sometimes curable disorder, the opportunities are tremendous for those marketing commercial aldosterone assay methods (already widely available), and even more so for automated aldosterone assays that offer simplicity, speed, and the opportunity to reduce technician time and/or numbers. Hence, in the midst of a revival in interest in primary aldosteronism and aldosterone measurement, there has been a recent move toward automation of the aldosterone assay, driven primarily by considerations of convenience, cost, or profit. By comparing 2 assay methods and 1 automated method with their more laborious but established in-house assay, which places accuracy and specificity over speed and simplicity, the authors provide a very valuable service(1). Importantly, the commercial assays were found wanting in several critical areas.Schirpenbach et al. have demonstrated marked differences in mean values among the 4 different assay methods. High “ r ” values were obtained, but it is of course widely known that correlations between results achieved by 2 methods have little bearing on accuracy. Nevertheless, some authors still place emphasis on them, which …