A critical appraisal of the radiological evaluation of nephrocalcinosis

The level of agreement concerning the diagnosis of nephrocalcinosis (NC) based on ultrasonography (US), computed tomography (CT) or kidney/ureter/bladder (KUB) X-ray was assessed.

Sequences of KUB+US+CT from 62 patients, 48 with at least one exam suggesting NC and 14 with pelvicalyceal calcifications (nephrolithiasis) were reviewed twice by 3 radiologists (firstly randomized and secondly presenting KUB+US+CT of each patient together).

The intraobserver concordance varied from 76 to 90% for KUB, 77 to 85% for US and 82 to 89% for CT. There was a significant change in diagnosis between the 1st and 2nd reviews for observer 1 in KUB and CT, for observer 2 in US, but not for observer 3. Evaluating patients' exams together did not provide a better agreement. The highest sensitivity and specificity (92 and 89%, respectively) were only attained when 2 exams suggested NC diagnosis, being CT one of them. These enabled us to suggest that 33 out of 48 (62.5%) patients had NC (evidenced in US+CT+KUB (81.8%), US+CT (12.1%) or KUB+CT (6.1%).

The low level of concordance renders the radiological diagnosis of NC difficult. Nephrocalcinosis should be confirmed by CT combined with either US or KUB.