Geographic location is an important determinant of risk factors for stone disease

Some regions are known to have an increased burden of urolithiasis. Urolithiasis is known to be affected by weather patterns, particularly high ambient temperatures. To identify geographic differences in risk factors, we compared metabolic information for 1254 patients in two geographically distinct regions, New York and Florida, with per sample adjustment for ambient weather. We observed that patients in New York were more likely to have low urine volume, but also lower total urinary calcium (168 vs 216 mg, p = 0.005), urate (376 vs 678 mg, p < 0.001), and phosphate (0.8 vs 0.9 g, p 0.007). Temperature was a predictor of urine pH (B = -0.07, p = 0.024). Geographic region was a predictive factor (p < 0.01) for urine calcium, volume, serum bicarbonate, and anion gap. Increased anion gap and serum HCO₃^- were also predicted by temperature (B = 0.065, p = 0.035). Interestingly, urine volume was not affected by temperature. Our finding that temperature is a determining factor of urine pH and anion gap may help to explain the finding that hot weather is associated with increases in urolithiasis. Anion gap has also been previously associated with poor health measures and represents an interesting target for future research. Geographic location may independently contribute to urine composition, through regional diets, sun exposure, and groundwater. This study highlights the impact geographic location plays in determining risk factors for stone disease and the value of regional knowledge to the treating physician in preventing stone disease.