Effect of age on diagnostic usefulness of stimulated plasma renin activity and saralasin test in detection of renovascular hypertension.

The diagnostic usefulness of the timed intravenous pyelogram (IVP), isotopic renal flow study (renal flow), stimulated plasma renin activity (SPRA), saralasin infusion test, and renal vein renins (RVR) in detecting possible renal vascular hypertension was studied in relation to age. Among patients who had been off medication for 2 weeks and who had normal renal X-ray findings, the percentage of those with a high SPRA dropped from 22.3% in those aged 20-29 to 4.2% in those aged 60-69 years, and that in those showing a positive saralasin test dropped from 8.3% in those aged 20-29 to 4.3% in those aged 60-69. But among those with abnormal renal X-ray findings, the percentage rose from 5.7% to 20% (high SPRA) and from 16.3% to 33% (positive saralasin test). A high SPRA or positive saralasin detected a renal abnormality in 11.7% and 50%, respectively, of patients aged 20-29, and 75% and 85.7%, respectively, of those aged 60-69. The percentage of all patients on or off medication with abnormal renal X-ray findings and a renal vein renin ratio > 1.5 increased from 14.2% among those aged 20-29 to 84.2% among those aged 60-69. The results indicate an increasing usefulness with age of a high SPRA or a positive saralasin test in indicating an abnormal renal X-ray and an abnormal renal vein renin ratio, and thus a potentially correctable lesion.