Computed tomography and ultrasonography: a comparative study in the diagnosis of analgesic nephropathy

Computed tomography (CT) and ultrasonography (US) were performed in 40 patients who had consumed excessive quantities of analgesics (> 1 kg) to compare their value in the diagnosis of analgesic nephropathy (AN). The computed tomography and sonographic features were renal papillary calcifications. Renal papillary necrosis (RPN) was documented in 20 of 40 patients by US and in 14 of 40 patients by CT. In 11 patients, both US and CT were positive. In 9 patients, US was positive whilst CT was negative. In 3 patients, CT was positive whilst US was negative. Prevalence of RPN was 50% using US and 35% using CT. Using US as a gold standard, sensitivity of CT was 55%, specificity 85%, positive predictive value 78.6% and negative predictive value 34.6%. Percent agreement with CT and US was 70%. Cohen's kappa statistic adjusting for chance agreement was 40%. Based on these results, it is found that US yielded a higher percentage of positive cases of RPN.