Sleep posture and unilateral renal stone formation

Abstract

Until now, there has been no hypothesis to explain the aetiology of recurrent unilateral urolithiasis in stone formers. Previous studies suggested that sleep posture may lead to alterations of renal haemodynamics. The probable association between sleep posture and unilateral urolithiasis is reported here. In this prospective cohort study, 38 patients with recurrent unilateral renal stones and 42 healthy controls were studied. Background variables were evaluated using a questionnaire. Sleep posture was recorded with a sleep recorder. Unpaired t test, Mann-Whitney test, and chi-squared test were performed as needed and p<0.05 was considered significant. Of 17 patients with right kidney stones, right-side-down sleep posture was seen in 15 (88.2%) and supine/prone in two (11.8%). Of 21 patients with left kidney stone, sleep posture was left-side-down in 13 (61.9%), right-side-down in two (9.5%) and supine/prone in six (28.6%, p=0.0). That is, a significant association was found between lateral sleep posture and ipsilateral kidney stone formation [odds ratio (OR)=21.13 for left-side, 95% confidence interval (CI) 4.16-123.8; and OR=21.14 for right-side, CI 95% 3.6-160.4]. Although the impact of sleep posture in recurrent unilateral stone formation remains unclear, sleep posture may play a causative role in promotion of urolithiasis. Although this observation needs further investigation, further studies should be conducted on the efficacy of appropriate education and learning to increase patients' capability to change routine sleep posture.