Is brain natriuretic peptide a reliable biomarker of hydration status in all peritoneal dialysis patients?

BACKGROUND Achievement of euvolemia is a fundamental challenge in the peritoneal dialysis (PD) population. Bioimpedance spectroscopy (BIS) is one of the best techniques for routine assessment of hydration status (HS) in PD, but in recent years, the role of brain natriuretic peptides (BNP) in the assessment of volume status has gained interest. The aim of this study was to investigate the relation between BNP and volume status as measured by BIS in PD patients and to assess how these variables correlate according to the time that a patient has been on PD. METHODS We prospectively studied 68 PD patients from whom measurements of BNP and assessments of HS by BIS were performed every 3 months. Three groups were defined based on HS: group A, measurements of HS <-1.1 liters (underhydrated); group B, measurements of HS between -1.1 and +1.1 liters (normohydrated), and group C, measurements of HS >+1.1 liters (overhydrated). Measurements were also separated according to the time on PD (<6 vs. ≥6 months). Correlation between HS and BNP was performed using Spearman's correlation. RESULTS We performed a total of 478 measurements of HS and BNP. There was a statistically significant difference in BNP (p < 0.001) among three HS groups, with higher levels of BNP detected in overhydrated patients. We found a positive correlation between HS and BNP (rs = 0.28; p <0.001) that seemed stronger in the first 6 months on PD (rs = 0.42; p = 0.006). CONCLUSIONS BNP correlated positively with fluid overload measured by HS, and this correlation was stronger in the first 6 months on PD.