Estimation of the efficacy of the measurement of plasma renin activity and direct renin in diagnostics of primary aldosteronism

Abstract

The objective of the present study was to estimate the informative value of the measurements of aldosterone level, direct renin, and plasma renin activity as well as the relationships between these characteristics for differential diagnostics of various forms of hypertension and, first and foremost, of primary aldosteronism. We have examined a total of 162 patients. The results of differential tests were used to allocate them to a few groups including 41 patients presenting with primary aldosteronism, 52 ones with incidentalomas, 26 with essential hypertension, and 43 with various endocrine diseases and normal arterial pressure (control groups). The aldosterone levels, direct renin, and plasma renin activity were measured in blood samples taken in morning hours from the patients in the supine position. The aldosterone to plasma renin activity (A/PRA) and aldosterone to direct renin (A/DR) ratios were calculated. The elevated blood aldosterone level is currently believed to be the principal criterion for primary aldosteronism in the patients suffering arterial hypertension. The RIA technology is the method of choice for the measurement of aldosterone levels. The determination of the A/PR ratio significantly improves the detectability of the disease. The use of direct renin level instead of kinetic renin ensures the high efficacy of screening for primary aldosteronism and its early diagnostics. The cut-off point for the calculation of the A/PRA ratio to differentiate between primary aldosteronism and incidentalomas is 2160 pmol/mcg/hr (sensitivity 100%, specificity 97.8%) in comparison with the analogous cut-off point for the discrimination between primary aldosteronism and endocrine pathology without hypertension is 49 pmol/mU (sensitivity 100%, specificity 95%). The cut-off point for the calculation of the A/PR ratio to differentiate between primary aldosteronism and incidentalomas is 2160 pmol/mcg/hr (sensitivity 89.5%, specificity 99%) in comparison with the analogous cut-off point for the discrimination between primary aldosteronism and endocrine pathology without hypertension is 1432 pmol/mcg/hr (sensitivity 89.5%, specificity 100%). It is concluded that the results of determination of direct renin level in the blood plasma are independent of the endogenous angiotensinogen level, less variable and more reproducible than than the results of the measurement of plasma renin activity. The aldosterone to direct renin ratio may be used for the screening of primary aldosteronism.