Measurement of the Renin-Angiotensin System

Abstract

Renovascular disease irrespective of the cause activates multiple pressor systems, most specifically the renin-angiotensin-aldosterone system (RAAS). This complex hormone system exerts several renal and vascular effects, and seminal studies have outlined the sentinel importance of this system in the context of renovascular disease. Experiments using Goldblatt’s classic 2 kidneys-1-clip model generate the prototype of angiotensin-dependent hypertension (Laragh, Am J Hypertens 4:541S–545S, 1991; Pickering, Semin Nucl Med 19:79–88, 1989). In humans, numerous methods to assess the levels of these hormones in the plasma have been proposed to characterize the hemodynamic significance of renovascular disease and to provide guidance on who will benefit of revascularization. However, in recent years, many of these diagnostic methods have been abandoned due to complex work-up, relatively low sensitivity and specificity, and the advent of more reliable non-invasive imaging techniques (Covic and Gusbeth-Tatomir, Prog Cardiovasc Dis 52:204–208, 2009). Although one could argue that the pressure in identifying the pressors roles has decreased, since preservation of function has become the most predominant argument, still, characterization of the RAAS system is important since it may provide useful additional information, including those for important therapeutic decisions.

Several screening laboratory tests have been proposed over the years to identify patients with renovascular hypertension. Some of these studies remain based on the identification of the activation of the RAAS system and some may depend on the comparison of the kidneys side-by-side assuming that one kidney is not affected. However, even under the best conditions, these studies are rarely more than 80 % sensitive or specific. As a result, their value as predictors depends greatly on the pretest probability of renovascular disease. Moreover, functional tests are heavily dependent upon test conditions, including volume status, sodium intake and antihypertensive medications, which can affect levels of this complex hormone system.