Captopril-enhanced scintigraphy using the method of the expected renogram: improved detection of patients with renin-dependent hypertension due to functionally significant renal artery stenosis.

PURPOSE AND DESIGN OF STUDY: Asymmetric-induced changes of the renogram under angiotensin-converting enzyme inhibition (ACE-i), i.e. lateralization, is probably the most distinctive finding for the detection of haemodynamically significant renal artery stenosis (RAS) in compensated kidney, since bilateral and symmetric patterns are non-specific. In the Consensus statement of diagnostic criteria of renovascular hypertension with captopril renography (Am J Hypertens 1991; 4: 749-755S) ACE-i-induced asymmetry of renograms for the left and right kidney was viewed as vitally important. However, detection of change in split function is a reliable parameter only when using a glomerular tracer, i.e. 99mTc-DTPA. No indication regarding a more widely used tubular tracer such as 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) has been given. METHODS AND RESULTS: The theoretical contralateral curve, called 'expected renogram', was calculated frame by frame from renal curves obtained under ACE-i and one of two baseline curves. The expected renogram was compared with the recorded ipsilateral curve. More than +/- 2 SD difference between expected and recorded renograms was assumed as suggestive of monolateral or bilateral RAS. Twenty-nine patients with angiographically proven RAS (bilateral in 12) and 20 patients without arteriographic evidence of stenosis were evaluated by postcaptopril/baseline 99mTc-MAG3 renography. Results obtained with the expected renogram analysis were compared with those obtained by standard criteria which included: improvement of peak time under baseline conditions, wash-out (75%) time, and monolateral or bilateral residual cortical activity > 10%, but asymmetrical, i.e. with > 5% change in split function. Compared to the standard evaluation, the use of the expected renogram for the diagnosis of RAS improved the specificity from 70 to 95% (P < 0.03) without loss of sensitivity (79.3%). Follow-up data after revascularization were available in 18 scintigraphically positive and six scintigraphically negative patients with RAS. The sensitivity of the expected renogram method referring to short-term (1 month) patient outcome following revascularization was 88.8%. The beneficial effects on blood pressure response persisted in 77% of the these patients at 18 months. Notably, four of six scintigraphically negative patients with RAS did not show any short-term benefit from revascularization and the improvement in blood pressure values lasted for 18 months in only one case. CONCLUSIONS: The high specificity of the expected renogram method reduces the number of unnecessary invasive procedures. This is a critical point for a low-prevalence disease such as renovascular hypertension.