Background

Management of hydration status in dialysis patients is a great challenge to nephrologists, and new tools to understand the hydration status (HS) are needed. The aim of this study was to investigate the usefulness of brain natriuretic peptide (BNP), analyzed bedside, as a marker of overhydration (OH) in hemodialysis (HD) patients.

Methods

We investigated the distribution of BNP, measured by Alere Triage® BNP Test, and analyzed the correlation between BNP and HS, defined by bioimpedance spectroscopy (BIS) in 64 HD patients. We assumed there would be a difference in HS between patients with high levels of BNP (h-BNP) and low levels of BNP (l-BNP) and choose an arbitrary cut off of 500 ng/ml, and then differences between the groups were tested for significance. HS, blood pressure (BP) and heart rate was measured, and BNP analyzed, before one mid-week dialysis session. Blood samples were also drawn for analysis of NT-proBNP and inflammatory markers. Demographic data, comorbidities, lab values and nutritional status were collected from medical records.

Results

A positive correlation was found between BNP and OH (r = 0.4), although many severely overhydrated patients had normal or just slightly elevated BNP. BNP levels were above 500 in 38 % (n=24) of the participants. The level of OH before dialysis was higher in the h-BNP group than in the l-BNP group. There was no difference in BP before or after dialysis, but patients in the h-BNP group were older, had lower muscle strength and lower Hemoglobin and Albumin levels compared to the l-BNP group.

Conclusion

A normal BNP does not rule out OH as defined by BIS in HD patients, on the other hand euvolemia was rare in patients with elevated BNP. This suggests that BNP might serve as a marker of OH in a subgroup of old and frail patients. In a further study we aim to investigate if the relationship between BNP, when elevated, and OH is reproducible at an individual level.