#2241 Validation of a new formula for total body water in peritoneal dialysis patients

Abstract

Abstract Background and Aims Peritoneal dialysis (PD) adequacy, assessed primarily by Kt/V, is crucial in routine clinical practice for detecting issues with PD treatment. This metric relies on urea levels and its volume (V) distribution, classically equivalent to total body water (TBW). TBW estimation, commonly achieved through the Watson and Watson (WW) formula, lacks dialysis patients in its original study, it also excluded patients with water metabolism disturbances, raising concerns about its generalizability to this population. Responding to this need, a new formula (NF) for calculating TBW in PD patients was developed in our center, with the aim of improving the correlation between administered Kt/V and clinical outcomes. Consequently, this study seeks to validate the proposed formula by applying it to a population. Method A prospective study conducted at a single center within PD program involved the collection of data on adequacy and Body Composition Monitoring (BCM) spanning from May 2023 to January 2024. TBW was calculated using the WW formula and the proposed new formula (TBW BI=0.36*Height+0.241*weight−9.675*BSA−26.234 for man and TBW BI=0.36*Height+0.241*weight−9.675*BSA−28.926 for woman). Categorical variables are presented as frequencies and percentages, continuous variables as means and standard deviations, or medians and interquartile ranges for variables with skewed distributions. A p-value < 0.05 was considered significant. Both formulas were subjected to correlation analysis with BCM TBW to assess mean differences using a paired-samples T test. Additionally, the resulting Kt/V values were compared, along with an examination of concordance in the detection of Kt/V values below 1.7. Results 66 measurements were collected from 36 PD patients. 29.2% (n = 10) were female, and the mean age was 59.7 years. Both formulas exhibited strong correlations with BCM TBW (WW: ρ = 0.949 and NF: ρ = 0.953, p < 0.001). BCM TBW showed a significant difference from WW TBW (34.8 vs. 38.1 liters, p < 0.001), but not when compared to the new formula (34.8 vs. 33.9, p = 0.06). The resulting BCM-derived Kt/V significantly differed from both formulas, with a larger mean difference compared to the WW formula (BCM: 2.71 vs. WW: 2.42, p < 0.001, and vs. the new formula: 2.77, p = 0.04). There was a perfect association between the use of NF and identification of BCM derived KtV measurements under the 1.7 target (Phi = 1, p < 0.001), an association that was strong for WW (Phi = 0.69, p < 0.001). Conclusion Errors in quantifying PD adequacy can lead to delayed detection of technical issues or inappropriate adjustments to already adequate prescriptions. We present a novel formula, specific for the PD population, reducing errors in PD quantification, particularly in settings where BCM is not available.