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Despite being recommended by most guidelines, the metabolic evaluation of patients with nephrolithiasis has limited diffusion due to difficulties relating both to the access to laboratory investigations and to urine collection modalities. Consequently, in addition to the classical 24-h collection, alternative and simplified collection modes have been proposed. We report here on the comparison between metabolic evaluation carried out on 24-h double collection (Lithotest) and overnight spot urines (RF test). Fifty-four patients with stone disease were enrolled, excluding patients with infection or cystine stones. For Lithotest, we measured all analytes necessary to calculate state of saturation (ß) with calcium oxalate, brushite and uric acid, by means of Lithorisk.com. For RF, we measured calcium, magnesium, oxalate, citrate, sulphate, phosphate, pH and creatinine. The comparison was made with creatinine ratios. An estimate of ßCaOx, ßbrushite and ßAU was obtained also on RF urines by using simplified algorithms. We found highly significant correlations between all parameters, despite quite different means. There was a nice correspondence between the two sets of measurements, assessed by the Bland-Altmann test, for calcium, oxalate, citrate, sulphate, urate and pH. Overnight urine had higher saturations compared to 24-h one owing to higher concentration of the former. In conclusion, RF test on overnight urine cannot completely replace Lithotest on 24-hr urine. However, it can represent a simplified tool for either preliminary evaluation or follow-up of patients with stone disease.

Background and objectives: Although 24-h urinary measure to estimate sodium and potassium excretion is the gold standard, it is not practical for large studies. We compared estimates of 24-h sodium and potassium excretion from a single morning fasting urine (MFU) using three different formulae in healthy individuals. Methods: We studied 1083 individuals aged 35–70 years from the general population in 11 countries. A 24-h urine and MFU specimen were obtained from each individual. A subset of 448 individuals repeated the measures after 30–90 days. The Kawasaki, Tanaka, and INTERSALT formulae were used to estimate urinary excretion from a MFU specimen. Results: The intraclass correlation coefficient (ICC) between estimated and measured sodium excretion was higher with Kawasaki (0.71; 95% confidence interval, CI: 0.65–0.76) compared with INTERSALT (0.49; 95% CI: 0.29–0.62) and Tanaka (0.54; 95% CI: 0.42–0.62) formulae (P <0.001). For potassium, the ICC was higher with the Kawasaki (0.55; 95% CI: 0.31–0.69) than the Tanaka (0.36; 95% CI: -0.07 to 0.60; P <0.05) formula (no INTERSALT formula exists for potassium). The degree of bias (vs. the 24-h urine) for sodium was smaller with Kawasaki (+313 mg/day; 95% CI: +182 to +444) compared with INTERSALT (-872 mg/day; 95% CI: -728 to -1016) and Tanaka (-548 mg/day; 95% CI: -408 to -688) formulae (P <0.001 and P = 0.02, respectively). Similarly for potassium, the Kawasaki formula provided the best agreement and least bias. Blood pressure correlated most closely and similarly with the 24-h and Kawasaki estimates for sodium compared with the other two formulae. Conclusion: In a diverse population, the Kawasaki formula is the most valid and least biased method of estimating 24-h sodium excretion from a single MFU and is suitable for population studies.

Background and objectives: Although 24-h urinary measure to estimate sodium and potassium excretion is the gold standard, it is not practical for large studies. We compared estimates of 24-h sodium and potassium excretion from a single morning fasting urine (MFU) using three different formulae in healthy individuals. Methods: We studied 1083 individuals aged 35–70 years from the general population in 11 countries. A 24-h urine and MFU specimen were obtained from each individual. A subset of 448 individuals repeated the measures after 30–90 days. The Kawasaki, Tanaka, and INTERSALT formulae were used to estimate urinary excretion from a MFU specimen. Results: The intraclass correlation coefficient (ICC) between estimated and measured sodium excretion was higher with Kawasaki (0.71; 95% confidence interval, CI: 0.65–0.76) compared with INTERSALT (0.49; 95% CI: 0.29–0.62) and Tanaka (0.54; 95% CI: 0.42–0.62) formulae (P <0.001). For potassium, the ICC was higher with the Kawasaki (0.55; 95% CI: 0.31–0.69) than the Tanaka (0.36; 95% CI: -0.07 to 0.60; P <0.05) formula (no INTERSALT formula exists for potassium). The degree of bias (vs. the 24-h urine) for sodium was smaller with Kawasaki (+313 mg/day; 95% CI: +182 to +444) compared with INTERSALT (-872 mg/day; 95% CI: -728 to -1016) and Tanaka (-548 mg/day; 95% CI: -408 to -688) formulae (P <0.001 and P = 0.02, respectively). Similarly for potassium, the Kawasaki formula provided the best agreement and least bias. Blood pressure correlated most closely and similarly with the 24-h and Kawasaki estimates for sodium compared with the other two formulae. Conclusion: In a diverse population, the Kawasaki formula is the most valid and least biased method of estimating 24-h sodium excretion from a single MFU and is suitable for population studies.