We investigated the possibility that variability in classification of patients with essential hypertension into low, normal, or high renin activity subgroups depends on the subject preparation that precedes the measurement of plasma renin activity (PRA). In 47 essential hypertensives, PRA was measured with patients supine and ambulatory who were receiving both an unrestricted dietary sodium intake and a low sodium diet. Additionally, PRA was determined following salt restriction, oral furosemide therapy, and ambulation. These results were compared, using several analytical techniques, to those of a group of age-, race-, and sex-matched normotensive controls. Extreme variability in classification was the rule, with only 28% of patients consistently classified as having normal PRA. No single approach provided maximal detection of both the low and high renin states. We conclude that renin classification of hypertensive patients requires a matched control population and that subtyping appears to be variable depending on diet, posture, and analytical approach.
(Arch Intern Med 138:1514-1519, 1978)