How is captopril renal scintigraphy used to evaluate for renal artery stenosis?
A renal scan in a patient with renal artery stenosis often appears normal because the renin-angiotensin system causes a vasoconstriction of the efferent arterioles, which helps maintain the pressure across the glomeruli, preserving renal function. A renal scan performed after the administration of captopril or other ACE inhibitor reveals abnormal flow and function because the regulatory mechanism of angiotensin is blocked by the ACE inhibitor. A scan using 99m Tc DTPA after captopril should show evidence of diminished flow and function in a kidney with renal artery stenosis compared with a renal scan without captopril. Generally, the overall sensitivity and specificity of this test are approximately 90% and 95%, respectively. With the advent of magnetic resonance angiography (MRA), there has been considerably less use of captopril renal scintigraphy, but it is still sometimes helpful to evaluate the functional significance of partially stenotic renal arteries.