Differentiation between renovascular and essential hypertension by means of changes in single kidney 99mTc-DTPA clearance induced by angiotensin-converting enzyme inhibition

The true clinical significance of renography in nephro-urology

Isotopic renography is a non-invasive technique used routinely by the clinician to provide information about kidney structure and function. Whilst there is no doubt of its value in the accurate measurement of glomerular filtration rate and in the detection of parenchymal abnormalities, its role in the diagnosis of renovascular disease (especially in patients with renal insufficiency), the exclusion of obstruction and the evaluation of the patient with either acute renal failure or renal transplant dysfunction remains unproven. In part, this reflects a failure to standardise protocols and rigorously evaluate diagnostic techniques. Recent developments in ultrasound, computerised X-ray tomography and nuclear magnetic resonance now present the clinician with rival techniques and emphasise the need for the clinical development of isotopic renography.

Diagnosing renal artery stenosis: a comparison between conventional renography, captopril renography and ultrasound Doppler in a large consecutive series of patients with arterial hypertension

The purpose of the study was to compare the positive and negative predictive values of conventional renography (Reno-A), captopril renography (Reno-B) and ultrasound Doppler (UD) with regard to the diagnosis renal artery stenosis. These three tests, and in addition a renal angiography, were performed in consecutively admitted patients with arterial hypertension, owing to either suspicion of renovascular hypertension or refractoriness to treatment. Patients with occlusion of a renal artery or a serum creatinine level higher than 300 mumol/l, or a previous investigation for renovascular hypertension at another hospital, were excluded from the analysis. The European Multicenter Study (EMS) criteria and local criteria for abnormal renography were compared. Of 131 patients, 28 had a renal artery stenosis (RAS) exceeding 50% reduction in diameter of the artery and 19 exceeding 70%. Using the EMS criteria for renography the predictive values of a negative test for a RAS more than 50% were 0.88 for Reno-A, 0.90 for Reno-B, 0.86 for changes from Reno-A to Reno-B, 0.92 for abnormalities either in Reno-A, Reno-B or changes from Reno-A to Reno-B, and 0.91 for UD. The corresponding values for a RAS more than 70% were 0.94, 0.97, 0.93, 0.98 and 0.96, respectively. The predictive values of a positive test were clearly lower, ranging from 0.20 to 0.75, but best when changes from Reno-A to Reno-B were used, 0.69-0.75. Using local criteria for renography the predictive values of a negative test were almost equal to those obtained by using the EMS criteria, but the predictive values of a positive test were slightly lower. It is concluded that conventional renography, captopril renography and ultrasound Doppler all are very good screening tests for renal artery stenosis, but the positive predictive values are clearly highest when using changes from conventional renography to captopril renography. It is suggested that captopril renography always should be performed when conventional renography is abnormal and vice versa to obtain the highest positive predictive value, on the assumption that total renal function is normal or almost normal, and that renal function is not absent in the affected kidney.

Simplified captopril renography in diagnosis and treatment of renal artery stenosis

To improve the diagnosis and forecast the response to surgery or renal angioplasty in patients with hypertension and renal artery stenosis, we employed a simplified captopril renography protocol in conjunction with renal arteriography in 94 clinically selected patients. Fifty hypertensive patients (group 1) with a high clinical likelihood of renovascular hypertension were evaluated using a simplified captopril renography protocol and renal angiography on the arterial side. Criteria for normal captopril renal scintigrams were established based on this original cohort and validated in an additional 44 clinically comparable patients (group 2). Renal revascularization or nephrectomy was performed in 39 patients, and success of the procedure was determined in the 34 patients for whom 3-month follow-up was available. In the 94 patients, 44 (47%) had renal artery stenosis. Simplified captopril renography was 91% sensitive and 94% specific in identifying or excluding renal artery stenosis in the combined group, with no difference in the diagnostic utility between groups 1 and 2, or in those with renal insufficiency (n = 38) or those with bilateral disease (n = 17). Scintigraphic abnormalities induced by captopril were strongly associated with cure or improvement in blood pressure control following revascularization or nephrectomy (15 of 18), while the lack of captopril-induced changes was associated with failure of such intervention (13 of 16) (p = 0.0004). We conclude that simplified captopril renography is highly sensitive and specific in the diagnosis of renal artery stenosis in a clinically selected high-risk population and that the test accurately predicts the success or failure of therapeutic intervention.

The role and rationale of nuclear medicine procedures in the differential diagnosis of renovascular hypertension

The use of radionuclides in the differential diagnosis of renovascular hypertension has gone through many periods of enthusiasm and of disappointment. Regardless of the problems with the routine renogram, the availability of gamma camera renal evaluation makes possible meaningful preintervention of screening. The use of the test as a follow-up procedure is an extremely important but often overlooked application of radionuclides in the evaluation of renovascular hypertension. The radionuclide technique is a sensitive and accurate method of evaluating the results of percutaneous angioplasty or surgery or renal function in the affected kidney of patients with renovascular disease. A major change in our approach to the nuclear medicine diagnosis of renovascular hypertension has been the introduction of captopril renography. Although there is still a great deal of work to be done and many investigators are actively studying captopril renography, the potential of the test is clear. Captopril renography should include a baseline renogram, followed by the administration of 25 mg of captopril and a repeat study. Specificity and sensitivity data on this test probably will not be available for several years, but preliminary results are encouraging enough to justify routine use at this time in clinics in which screening for renovascular hypertension is carried out.