Increased renal papillary density in kidney stone formers detectable by CT scan is a potential marker of stone risk, but is unrelated to underlying hypercalciuria

Several previous studies have reported an increase in Hounsfield unit density of the renal papillae in patients with nephrolithiasis compared with controls. Kidney stone formers (KSF) were found to have higher papillary and cortical density in both kidneys, irrespective of which side had calculi, and it was proposed that this might be related to the presence of underlying hypercalciuria. The current study was designed: (1) to determine whether recurrent KSF do have higher papillary density compared with healthy controls; (2) to test an association between higher renal papillary density and the presence of hypercalciuria in KSF. This retrospective case-matched controlled study was carried out at the Royal Free Hospital, London, UK. We investigated 111 patients, 57 of whom were KSF and 54 healthy controls. The CT attenuation values were measured within a 0.2 cm2 area of the renal papilla in the upper, middle, and lower segments of each kidney, and were compared between KSF and non-stone formers, and between KSF with and without hypercalciuria. There were no significant differences in age and sex between groups. Papillary density was significantly higher in KSF by both crude and adjusted analyses (p < 0.001). However, there was no association between higher papillary density and hypercalciuria in KSF. The papillary density measured by CT is a useful, non-invasive tool to differentiate between KSF and healthy controls. The absence of any correlation between papillary density and hypercalciuria suggests that the presence of clinically significant underlying renal stone disease, rather than urinary metabolic abnormalities, correlates with radiologically detectable increased papillary density.