Comparison of the Watson formula and bioimpedance spectroscopy for measuring body volume and calculating kt/V in patients with peritoneal dialysis

Abstract

Background: Ascertaining the total body water (V), usually obtained by the Watson formula or bioimpedance spectroscopy (BIS), is crucial for the calculation of Kt/V in patients with peritoneal dialysis (PD). The aim of our study was to compare two different methods of determining V and explore which one is suitable for clinical application.

Methods: This was a retrospective observational study. V was determined using the Watson formula (Vwat) and BIS (Vbis). The differences between Vbis and Vwat and between Kt/Vbis and Kt/Vwat were assessed. The patients were allocated to different groups according to the Kt/Vwat and Kt/Vbis values. Clinical parameters were compared between these groups to investigate which method of obtaining the Kt/V value was more suitable.

Results: 150 patients on PD were included. Vwat was significantly higher than Vbis, apart from in female patients with volume overload. Consequently, weekly Kt/Vwat was lower than Kt/Vbis in these patients. A significant negative correlation between mean Vwat-Vbis and overhydration values was also found. Moreover, through uniform manifold approximation and projection analysis, a clustering tendency between patients in the adequate group with both Kt/Vwat and Kt/Vbis > =1.7 and patients in the inconsistent group with Kt/Vwat <1.7 and Kt/Vbis > =1.7 was identified, suggesting that their clinical features were similar.

Conclusion

There were significant differences between Vwat and Vbis and between Kt/Vwat and Kt/Vbis. Kt/Vwat may underestimate small-solute dialysis adequacy in most cases. Kt/Vbis instead of Kt/Vwat could be accounted for in creating individualized dialysis prescriptions if the patient has no obvious clinical symptoms.

Keywords:

• peritoneal dialysis
• total body water
• Watson formula
• bioimpedance spectroscopy
• Kt/V

Acknowledgements

We are grateful to all participants and the nurses of the PD center for their efforts and contributions to this research.

Ethical approval

The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Ethical Committee of Nanjing Drum Tower Hospital (no. 2022-042-01).

Author contributions

Sixiu Liu, Yuan Feng and Chunming Jiang designed the study. Sixiu Liu and Yuan Feng collected the clinical data of patients and drafted the manuscript. Sixiu Liu performed statistical analyses. Jian Lu, Nan Li and Ying Liu checked and revised the article. All authors read and approved the final manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data underlying this article will be shared on reasonable request to the corresponding author.

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.