17 Patients with sustained diastolic hypertension caused by unilateral main or segmental renal artery stenosis, were evaluated with rapid sequence excretory urograms, renal angiography, split function studies and renal vein renin determinations. Of these 17 patients, 16 (94%) had adequate followup, and all were cured or improved by an operation. The diagnostic accuracy of the split function ratio and renal vein renin ratio was 88% (15 of 17), and 70% (12 of 17), respectively. In addition, the disparity between patients with renal vascular hypertension and those with essential hypertension was more clearly defined by the split function study. As a confirmatory test of unilateral renovascular hypertension in patients with radiographic evidence of renal artery stenosis, the split function study is clearly superior to the renal vein renin ratio. In patients with pyelonephritis, hydronephrosis or nonfunctioning kidneys, the renal vein renin ratio is the only means of diagnosing functionally significant renal ischemia. In the light of the technical difficulties present in the split function study and renal vein renin determination, the split function study is a more reliable test, and should most certainly be performed in any patient who may be denied a corrective renovascular operation because of a negative renal vein renin ratio. The patient's response to an operation can be predicted most accurately when the contralateral renal plasma flow, renal vein renin ratio and contralateral renin secretion are considered simultaneously.
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