Quantitative residual cortical activity measurement: Appropriate test for diagnosis of renal artery stenosis?

Objectives: To evaluate the diagnostic validity of quantitative measurement of residual cortical activity (RCA) in renal artery stenosis (RAS). Methods: In 45 patients with a high clinical likelihood of renovascular hypertension (RVH) and unimpaired renal function, dynamic imaging was performed after an intravenous bolus injection of 148 MBq Tc-99m MAG3 for both baseline renoscintigraphy and captopril renography following oral application of 50 mg captopril. RCA was measured according to the Sfa-kianakis method: RCA = cortical counts at 20 min/counts at peak x 100%. An increase in RCA of greater than or equal to 5% from baseline was considered indicative of RAS. After renography, all patients underwent selective transfemoral angiography with the digital subtraction technique. A luminal reduction of greater than or equal to 50% was considered as proof of RAS. Results: The number of kidneys that had a change of 15% in RCA values was 12 (27.2%) in normal kidneys, 7 (58.3%) in the patients with bilateral RAS, 14(82.3%) in the patients with unilateral RAS, and 21 (72.4%) in overall kidneys with RAS. The positive test ratio in pathologic groups was significantly higher than normal (p < 0.05). The sensitivity and specificity of the RCA test were 72.4 and 72.7%, respectively; the positive and negative predictive values were 63.6 and 80%, respectively. Conclusion: Quantitative measurements of RCA can be used as a diagnostic parameter of renal artery stenosis and may contribute of the diagnostic accuracy of visual interpretation and other renographic diagnostic criteria.