Prevalence

The true prevalence of RAS (all grades) is not known, but in an unselected hypertensive population, the prevalence of RAS runs between 1% and 5% (3-5). With such a low prevalence, screening for RAS may result in an unacceptably high false positive

Figure 1 Bilateral RAS. AP aortogram with the pigtail flush catheter positioned just above the level of the renal arteries. There are two right renal arteries and a single left renal artery. All have severe ostial stenoses (arrows). Notice that the left kidney is small; it was found to be very poorly functioning on renography. Abbreviations: RAS, renal artery stenosis; AP, anteroposterior.

Figure 1 Bilateral RAS. AP aortogram with the pigtail flush catheter positioned just above the level of the renal arteries. There are two right renal arteries and a single left renal artery. All have severe ostial stenoses (arrows). Notice that the left kidney is small; it was found to be very poorly functioning on renography. Abbreviations: RAS, renal artery stenosis; AP, anteroposterior.

rate. Performance would be improved by increasing the pretest probability of RAS by identifying a high-risk group to make "screening," or more accurately, case finding a cost-effective proposition. Those with vascular disease in other territories have a higher incidence of RAS. Harding et al. (6) found RAS in 30% of patients undergoing cardiac catheterization, and the relationship with peripheral vascular disease is even stronger, with studies quoting RAS rates of between 38% and 49% (7,8). The atherosclerotic patient who is also hypertensive has an even higher pretest probability of RAS, and the probability is further increased in those with severe hypertension. In the cooperative study (9) of renovascular hypertension, investigators compared 339 patients with essential hypertension with 175 patients with renovascular hypertension in order to identify the clinical findings most strongly associated with renovascular hypertension. Renovascular hypertension was characterized by advanced age, hypertension of short duration or accelerated hypertension, retinopathy, and the coexistence of cardiovascular, peripheral vascular, or cerebrovascular disease. Thus, clinical markers can allow more selective investigation of patients for RAS, improving the cost-effectiveness of any "screening" investigation: these clinical markers are shown in Table 1 and the grading of RAS is listed in Table 2.

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