To answer Dr. Spital's question with complete confidence would require data that are not currently available. Certainly, individual patients with impaired renal function due to renal artery stenosis can present without hypertension (see case 9 from Messina and coworkers [1]). In our experience, the observed normal or low blood pressure is most likely due to the use of drugs with antihypertensive effects for the treatment of angina or heart failure, although in some cases it appears to be due to severely depressed cardiac output. Most of these patients have a history of hypertension, but some do not.

We agree that renal failure resulting solely from renovascular disease would be unlikely to develop without hypertension in the patient who takes no medications and has an otherwise normal cardiovascular system. In experimental unilateral renal artery stenosis, however, hypertension can resolve. If such a state exists in a patient who is treated with converting enzyme inhibitors, calcium-entry blockers, or ß-blockers for a comorbid condition, hypertension may be lost as an indicator of progressive vascular disease when a contralateral renal artery lesion develops. We believe that unexplained progressive renal insufficiency in a patient with diffuse vascular disease should raise the question of renal artery stenosis whether or not hypertension is present.

We feel that the data from the study by Harding and colleagues [2] support the view that, within the group of patients with proven atherosclerotic vascular disease, a rather large number are "at risk" for renal disease due to renal artery stenosis. It is important to emphasize that even if renovascular disease were responsible for 15% of end-stage renal disease in the United States, this outcome would still be relatively rare in the general population (incidence, 27 cases per million). This observation, plus the lack of a difference in average renal function in the groups with and without renovascular disease noted by Dr. Spital, suggests that the disease uncommonly progresses to renal failure. Although we recommend intervention when renal insufficiency is progressive, we hope we conveyed our view that, in the absence of progressive renal disease or uncontrolled hypertension, the physiologic and prognostic importance of renal artery stenoses is uncertain, and we do not recommend trying to find or treat such lesions.