Ureteral catheterization studies.

It is apparent that the split function study and renal vein renin determination are complementary and afford valuable information for selecting patients with potentially curable renovascular hypertension. The split function study, when interpreted with the recently defined split function ratio, offers the clinician a highly accurate means of diagnosing significant renal ischemia. Because the split function ratio shows the disparity between the ischemic and contralateral kidney to a greater degree, the chance of misdiagnosis due to laboratory or physician error is minimized. The split function study, however, is of limited value in patients with pyelonephritis since the water- and salt-losing characteristics of the pyelonephritic kidney may mask significant renal ischemia. In these patients, as well as those with a nonfunctioning kidney or hydronephrosis, the renal vein renin determination is the test of choice. In addition, the added morbidity of the split function study is not warranted in a patient with an elevated peripheral renin which, for interpretation, requires an accurate 24 hour urine for sodium, a renal vein renin ratio outside the range of patients with essential hypertension (renal vein renin ratio greater than 1.7) and evidence of suppression of renin secretion from the contralateral kidney. If, however, the renin determination does not afford convincing evidence of significant renal ischemia in a patient with radiographic evidence of renal arterial stenosis, a split function ratio definitely should be determined to more completely define the pathology. The attendant morbidity of a carefully performed split renal function study does not approach the morbidity and mortality associated with unnecessary surgery or inadequately treated hypertension.