The pioneering work of Laragh, Sealey and their colleagues, widely confirmed by others, suggests instead that heterogeneity, in fact, characterizes patterns of blood pressure control in populations. This heterogeneity can be exposed through assessment of the activity of the renin angiotensin system (RAS). Specifically, volume and vasoconstriction determine blood pressure control. Patients in whom volume predominates have suppressed RAS, and, conversely, those in whom vasoconstriction predominates will have an activated RAS. This can be simply and accurately determined by estimation of plasma renin activity (PRA).