背景:CKD患者的盐摄入可影响心血管风险和肾脏疾病进展。24小时(24小时)尿液收集通常用于研究盐代谢,但执行起来很麻烦。我们评估了点尿液样本中的尿钠(U-Na)浓度,并研究了肾脏护理下CKD患者24hU-Na排泄和浓度的相关性。Further,我们研究了CKD分期和利尿剂的作用,并评估了从斑点尿液样本中预测24hU-Na排泄的常用公式的性能。
方法:纳入德国慢性肾脏病(GCKD)研究的108名患者。每个参与者在同一时期内收集了24小时尿液和两个斑点尿液样本。第一点尿样(AM)是第二晨尿的一部分。在晚餐前(PM)收集第二尿样。建议患者照常服药,不改变饮食习惯。两个斑点尿液样品中的U-Na浓度及其平均值((AMPM)/2)与24小时尿液中的U-Na浓度和总Na排泄相关。随后根据CKD分期和利尿剂摄入量进行分层后,研究了相关性。三个常用方程对从斑点尿液样本中估算24hU-Na排泄的有用性(川崎,Tanaka和Intersalt)是使用Bland-Altman地块确定的,敏感性分析,特异性,以及阳性预测值(PPV)和阴性预测值(NPV)。
结果:参与者(42名女性,66名男性)平均(±SD)62.2(±11.9)岁,平均血清肌酐为1.6(±0.5)mg/dl。95%有动脉高血压,37%为糖尿病,55%为利尿剂。对于PM斑点U-Na样品,发现与24hU-Na总排泄的最佳相关性。当比较斑点和24h尿U-Na浓度时,我们还发现了很强的相关性。校正U-肌酐的斑点U-Na并不能改善相关性的强度。既不是CKD阶段,利尿剂的摄入对这些相关性也没有显著影响。所有检查的公式都显示出明显的均值偏差。使用Tanaka公式获得了24小时内估计和测量的U-Na排泄之间的最低平均偏差和最强相关性。此外,田中公式与PMU-Na的应用提供了最佳的灵敏度,特异性,PPV和NPV估计U-Na排泄量>4g/d对应盐耗>10g/d。
结论:点尿样中的U-Na浓度与24hU-Na排泄相关,尤其是当使用PM点U-Na时。然而,相关系数相对较低。CKD阶段和利尿剂的摄入似乎都不会对这些相关性产生影响。所有测试的配方都存在显着偏差,其中Tanaka配方与测得的24hU-Na排泄具有最强的相关性。总之,在流行病学研究中使用点尿样和Tanaka公式似乎可以确定CKD患者盐摄入量与结局之间的相关性.然而,点尿样在指导和监测个别患者食盐消耗方面的作用仍然有限.
BACKGROUND: Salt intake in CKD patients can affect cardiovascular risk and kidney disease progression. Twenty-four hour (24h) urine collections are often used to investigate salt metabolism but are cumbersome to perform. We assessed urinary sodium (U-Na) concentration in spot urine samples and investigated the correlation with 24h U-Na excretion and concentration in CKD patients under nephrological care. Further, we studied the role of CKD stage and diuretics and evaluated the performance of commonly used formulas for the prediction of 24h U-Na excretion from spot urine samples.
METHODS: One hundred eight patients of the German Chronic Kidney Disease (GCKD) study were included. Each participant collected a 24h urine and two spot urine samples within the same period. The first spot urine sample (AM) was part of the second morning urine. The second urine sample was collected before dinner (PM). Patients were advised to take their medication as usual without changing dietary habits. U-Na concentrations in the two spot urine samples and their average ((AM + PM)/2) were correlated with U-Na concentration and total Na excretion in the 24h urine collections. Correlations were subsequently studied after stratification by CKD stage and diuretic intake. The usefulness of three commonly applied equations to estimate 24h U-Na excretion from spot urine samples (Kawasaki, Tanaka and Intersalt) was determined using Bland-Altman plots, analyses of sensitivity, specificity, as well as positive (PPV) and negative predictive values (NPV).
RESULTS: Participants (42 women, 66 men) were on average (± SD) 62.2 (± 11.9) years old, with a mean serum creatinine of 1.6 (± 0.5) mg/dl. 95% had arterial hypertension, 37% diabetes mellitus and 55% were on diuretics. The best correlation with 24h U-Na total excretion was found for the PM spot U-Na sample. We also found strong correlations when comparing spot and 24h urine U-Na concentration. Correction of spot U-Na for U-creatinine did not improve strength of correlations. Neither CKD stage, nor intake of diuretics had significant impact on these correlations. All examined formulas revealed a significant mean bias. The lowest mean bias and the strongest correlation between estimated and measured U-Na excretion in 24h were obtained using the Tanaka-formula. Also, application of the Tanaka-formula with PM U-Na provided best sensitivity, specificity, PPV and NPV to estimate U-Na excretion > 4g/d corresponding to a salt consumption > 10g/d.
CONCLUSIONS: U-Na concentration of spot urine samples correlated with 24h U-Na excretion especially when PM spot U-Na was used. However, correlation coefficients were relatively low. Neither CKD stage nor intake of diuretics appeared to have an influence on these correlations. There was a significant bias for all tested formulas with the Tanaka-formula providing the strongest correlation with measured 24h U-Na excretion. In summary, using spot urine samples together with the Tanaka-formula in epidemiological studies appears feasible to determine associations between approximate salt intake and outcomes in CKD patients. However, the usefulness of spot-urine samples to guide and monitor salt consumption in individual patients remains limited.