False-positive captopril renography in patients taking calcium antagonists

Captopril-enhanced renography is the noninvasive test of choice for the diagnosis of renovascular hypertension. Previous studies have shown that bilateral symmetrical changes are associated with many renal conditions. However, patients with normal renal angiography occurred in our institutions despite this scintigraphic pattern, and no known conditions could explain these results. The purpose of this study was to evaluate the diagnostic implications of bilateral symmetrical renal function deterioration on captopril renography.

Eighty-six captopril renal scintigraphies performed at two centers to exclude renovascular hypertension (50 consecutive patients after the observation of a bilateral symmetrical renal function deterioration despite a normal angiogram at one institution and 36 patients with both captopril renography and renal angiography at the other institution) were retrospectively reviewed. Baseline and captopril-enhanced renograms were obtained with 99mTc-mercaptoacetyltriglycine and a 1-day protocol in 50 patients; 36 patients were studied using 99mTc-diethylenetriamine pentaacetic acid and a 2-day protocol. Bilateral symmetrical renal function deterioration was detected.

Ten patients presented with bilateral symmetrical renal function deterioration on their captopril renograms; 9 of them were taking calcium antagonists (p=0.015). Control studies performed in 5 patients without these medications demonstrated normal captopril renograms in 4 and persistent renal dysfunction in 1. No explanation was found for the patient who was not taking any medication. Angiograms performed in 5 patients showed normal renal arteries. An 11th patient who was taking a calcium antagonist showed dysfunction of his one kidney on the captopril renogram but no artery stenosis on the renal angiogram.

Calcium antagonists can cause false-positive captopril renograms. These medications should be stopped before captopril renography, and physicians should be aware of this possible drug interaction if bilateral symmetrical renal function deterioration is seen on a patient's captopril renogram.