99mTc-DTPA candesartan renography in the diagnosis of renovascular hypertension

Aim: Captopril renography (CPR) has been proved to be highly accurate in the diagnosis of patients with renovascular hypertension (RVH). However, a false-negative rate up to 20% has been described. Candesartan, a new angiotensin II AT1-receptor antagonist (ARA), has proved to be more effective to lower blood pressure in hypertensive patients than losartan, the most widely used drug of the group. The aim of this study was to evaluate the feasibility and the potential clinical value of candesartan renography (CSR) in the diagnosis of RVH and to compare on a head-to-head basis, the results of CPR and CSR. Material and Methods: A total of 39 studies were performed on 14 patients (9 female, 5 male, median age 45.5 yr, range: 35-74 yr) with moderate-to-high risk of RVH, using a three-day protocol (1: CPR, 2: CSR, 3: baseline). If the CPR and CSR studies were normal, no further studies were done. A dose of 296 MBq of 99mTc-DTPA was i.v. injected one hour after captopril (50 mg), and three hours after candesartan (8 mg) interventions. Patients were imaged supine with a LFOV camera equipped with a LEHR collimator. Renogram curves were generated and split kidney uptake was also calculated during tracer uptake interval (2 to 3 min), using the area method. A study was considered of high probability for RVH (positive) when an unilateral change ≥2 in the renogram grade and/or a reduction in the relative kidney uptake greater than 10% was seen in the CPR/CSR study compared with the baseline acquisition. Patients underwent angiography (n=10) or colour doppler (n=4) within 2 weeks of nuclear studies. Results: Six patients were diagnosed by correlative imaging with unilateral (n=5) or bilateral (n=1) renal artery stenosis (RAS). In this group CPR was positive in 2/7 (29%) renal units whereas CSR was positive in 6/7 (86%). No evidence of significant RAS was demonstrated in the remaining group of patients (n=8) in whom CPR and CSR studies were negative for RVH. Conclusion: These preliminary results suggest that candesartan renography may be a sensitive test to diagnose patients with RVH. This finding could be related to a tight binding and a slow dissociation of candesartan from the angiotensin II AT1-receptor