Clinical characteristics in urolithiasis formation according to body mass index

Although urolithiasis is considered to be strongly associated with lifestyle habits, there are numerous cases in which urolithiasis develops despite a non-obese body type or healthy lifestyle habits. However, in clinical practice, the diet therapy and lifestyle changes instructed for the prevention of recurrence of urolithiasis are almost identical in numerous cases. Therefore, the present study examined the effect of body mass index (BMI) on urolithiasis and its surrounding environment in patients, by analyzing the number of normal- and high-BMI (healthy and overweight) patients with urolithiasis. The present study analyzed 63 patients with urolithiasis for whom height and weight were measured at our hospital (Tokyo Medical University Ibaraki Medical Center). BMI <25 represents healthy body types and BMI ≥25 BMI defines overweight body types. Thus, patients were then grouped by BMI-defined body type using a threshold value of 25 accordingly. It was observed that a higher percentage of males were obese compared with females. Upon comparing the normal- and high-BMI groups, no significant difference was observed in uric acid level, urine pH or calculus number between the two groups. Liver computed tomography (CT) values were significantly lower in the high-BMI group compared with the normal-BMI group. There was no significant correlation between calculus size counts and BMI. However, a significant negative correlation was observed between BMI and the liver CT value. These results suggest that liver CT values correlated negatively with BMI, but the data indicates that other mechanisms unassociated with a fatty liver may be involved in urolithiasis in non-obese patients. The results of the present study suggest that physicians should consider the mechanism involved in preventing the recurrence of urolithiasis.