Excretory urography and renal scintigraphy for chronic obstructed kidney: does nonopacity mean nonsalvageability?

INTRODUCTION This study aimed to ascertain whether nonopacified kidney on excretory urography (also known as intravenous urography [IVU]) indicates nonsalvageability. METHODS We retrospectively reviewed 45 adult patients with chronic unilateral urinary tract obstruction, in whom IVU revealed nonopacified kidney on one side but normal excretion on the contralateral side. Affected kidneys with split glomerular filtration rate (GFR) < 10 mL/min/1.73 m2 on 99mTc-diethylenetriaminepentaacetic acid diuretic renal scintigraphy were considered nonsalvageable. Non-function was defined based on cutoff points (< 15% and < 20%) to determine the sensitivity and specificity of differential renal function. Differences in IVU and renal scintigraphy findings, with respect to the duration of delayed filming on IVU, were analysed for significance. RESULTS The results of IVU and renal scintigraphy findings for 34 (75.6%) nonopacified kidneys matched, representing nonsalvageable kidneys. Sensitivity and specificity of differential renal function were 76% and 100%, respectively, when the cutoff point for non-function was set at < 15%. Sensitivity and specificity were 97% and 82%, respectively, when the cutoff point was < 20%. There was no significant difference between renal scintigraphy findings and IVU with 2-hour and > 2-hour delayed films (p = 0.96). CONCLUSION Although most nonopacified kidneys on IVU were nonsalvageable, a quarter of them were found to be salvageable on renal scintigraphy. Besides split GFR, differential function at cutoff point < 15% could be used to determine non-function of a chronic obstructed kidney when the contralateral kidney is normal. Delayed filming beyond two hours appears unnecessary in ensuring non-excretion on IVU.