Abstract
Estimated 24-hour urinary creatinine excretion (24 hrUCr) may be useful for converting spot urine analyte/creatinine ratio into estimated 24-hour urinary excretion of the evaluated analyte, and for verifying completeness of 24-hour urinary collections. We compared various published 24 hrUCr-estimating equations against measured 24 hrUCr in hospitalized hypertensive patients. 24 hrUCr was measured in 293 patients and estimated using eight formulas (CKD-EPI, Cockcroft-Gault, Walser, Goldwasser, Rule, Gerber-Mann, Kawasaki, Tanaka). We used the Pearson correlation coefficient, the Bland-Altman method, and the percentage of estimated 24 hrUCr within 15%, 30% (P30), and 50% of measured 24hUCr to compare estimated and measured 24 hrUCr. Differences between the mean bias by eight formulas were evaluated using the Friedman rank sum test. Overall, the best formulas were CKD-EPI (mean bias 0.002 g/d, P30 86%) and Rule (mean bias 0.022 g/d, P30 89%), although both tended to underestimate 24 hrUCr with higher excretion values. The Gerber-Mann formula and the Asian formulas (Tanaka, Kawasaki) were less precise in our study population but superior in an analysis restricted to subjects with highest measured 24 hrUCr per body weight. We found significant differences between 24 hrUCr-estimating equations in hypertensive patients. In addition, formula performance was critically affected by inclusion criteria based on measured 24 hrUCr per body weight.
Highlights
The study population included 293 patients who were admitted to our specialist tertiary care hypertension unit and had a 24-hour urine collection performed
We included all patients in whom creatinine was measured in 24-hour urine collection and necessary demographic and anthropometric data were available in the medical records
The 95% limits of agreement for the Bland-Altman approach, which indicate the range where the error of individual estimation lies within in 95% of cases, were calculated as the mean bias value ± 1.96 standard deviation of the mean bias
Summary
In the present study we aimed to compare various 24 hrUCr-estimating equations against measured 24 hrUCr, and indirectly against each other, in an unselected patient population admitted to a specialist hypertensive unit and undergoing routine inpatient clinical evaluation which provided an opportunity to obtain 24-hour urine collections for the reference measurement of 24 hrUCr
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