Temperature and relative humidity have opposing effects on evaporative water loss, the likely mediator of the temperature-dependence of nephrolithiasis. However, prior studies considered only dry-bulb temperatures when estimating the temperature-dependence of nephrolithiasis.

We used distributed lag non-linear models and repeated 10-fold cross-validation to determine the daily temperature metric and corresponding adjustment for relative humidity that most accurately predicted kidney stone presentations during hot and cold periods in South Carolina from 1997 to 2015. We examined three metrics for wet-bulb temperatures and heat index, both of which measure the combination of temperature and humidity, and for dry-bulb temperatures: (1) daytime mean temperature; (2) 24-h mean temperature; and (3) most extreme 24-h temperature. For models using dry-bulb temperatures, we considered four treatments of relative humidity.

Among 188,531 patients who presented with kidney stones, 24-h wet bulb temperature best predicted kidney stone presentation during summer. Mean cross-validated residuals were generally lower in summer for wet-bulb temperatures and heat index than the corresponding dry-bulb temperature metric, regardless of type of adjustment for relative humidity. Those dry-bulb models that additionally adjusted for relative humidity had higher mean residuals than other temperature metrics. The relative risk of kidney stone presentations at the 99th percentile of each temperature metric compared to the respective median temperature in summer months differed by temperature metric and relative humidity adjustment, and ranged from an excess risk of 8–14%. All metrics performed similarly in winter.

The combination of temperature and relative humidity determine the risk of kidney stone presentations, particularly during periods of high heat and humidity. These results suggest that metrics that measure moist heat stress should be used to estimate the temperature-dependence of kidney stone presentations, but that the particular metric is relatively unimportant.

温度和相对湿度对蒸发失水有相反的影响，蒸发失水可能是肾结石的温度依赖性介质。但是，先前的研究在估计肾结石的温度依赖性时仅考虑了干球温度。

我们使用分布式滞后非线性模型并重复进行10倍交叉验证，以确定每日温度指标和相对湿度的相应调整，以最准确地预测1997年至2015年南卡罗来纳州冷热期间的肾结石表现。湿球温度和热指数的三个度量标准，均用于测量温度和湿度的组合，以及干球温度的三个度量标准：（1）日间平均温度；（2）24小时平均气温；（3）最极端的24小时温度。对于使用干球温度的模型，我们考虑了四种相对湿度的处理方法。

在188,531名肾结石患者中，24小时湿球温度最能预测夏季出现肾结石。无论相对湿度的调整类型如何，夏季的湿球温度和热量指数的交叉验证平均残差通常都低于相应的干球温度度量。与其他温度指标相比，那些额外调整了相对湿度的干球模型具有更高的平均残差。在夏季，每个温度指标的第99个百分位数与相应中位温度相比，肾结石表现的相对风险因温度指标和相对湿度调整而异，其相对风险为8–14％。在冬季，所有指标的表现均相似。

温度和相对湿度的组合决定了出现肾结石的风险，特别是在高温高湿的时期。这些结果表明，应使用测量湿热应激的指标来估计肾结石表现的温度依赖性，但特定指标相对不重要。