Calcium channel blockers: a potential cause of false-positive captopril renography

The purpose of the study was to review the causes of false-positive and false-negative captopril Tc-99m MAG3 renograms performed to evaluate renovascular hypertension at the authors' institution.

From May 2000 to January 2002, 77 patients were referred for evaluation of possible renovascular hypertension with captopril Tc-99m MAG3 renography. If the findings of the captopril study were abnormal, a baseline study was performed 3 days later. The captopril studies were retrospectively reviewed and correlated with available renal arteriography, magnetic resonance angiography, and duplex Doppler sonography studies and clinical follow-up. Renal artery stenosis greater than 70% on an arteriogram and 60% on Doppler studies or magnetic resonance angiography was considered positive for renovascular hypertension.

There were five false-negative and four false-positive studies. The five patients who had the false-negative captopril studies underwent arteriography, which showed renal artery stenosis, and a stent was placed in two of them. The four false-positive captopril studies were proved by negative arteriograms in three and negative magnetic resonance angiography in one. Three patients with false-positive studies had bilateral renal function impairment after captopril and were taking calcium channel blockers at the time of the captopril study. One patient had a left nephrectomy and was also taking calcium channel blockers.

Chronic intake of calcium channels blockers is a potential cause of bilateral symmetric false-positive captopril renography.