Cardiac Biomarker Indicates Fluid Overload in Dialysis Patients

A new study has found that N-terminal pro-brain-type natriuretic peptide (NT-pro-BNP), a cardiac biomarker in dialysis patients, can also serve as a fluid overload biomarker for the management of patients with kidney disease.

Researchers at University College London (UCL; United Kingdom) determined the pre- and post-dialysis body volume status in 72 stable hemodialysis outpatients by multifrequency bioimpedance, and then established the determined value relationship measured to NTproBNP values. The patients also underwent tests of heart function.

The researchers found that the mean values of NTproBNP were 931.9 pmol/L (predialysis), compared to 242 pmol/L (postdialysis); on a simple correlation, the NTproBNP values were found to be associated with markers of volume overload and cardiac dysfunction. However, on logistical regression analysis, the strongest association was with the predialysis ratio of extracellular water to total body water, followed by postdialysis mean arterial blood pressure, dialysate calcium concentration, and change in extracellular fluid volume with dialysis. The researchers therefore concluded that NT-proBNP levels were most associated with indicators of fluid overload. The results of the study contrast with previous studies that suggest NT-proBNP might be a useful biomarker to predict increased risk of cardiovascular events and death in patients with kidney disease. The study was published ahead of print on May 27, 2010, in the Clinical Journal of the American Society of Nephrology (CJASN).

"Though this ‘cardiac biomarker' now appears to be more closely related to fluid status than to heart function, an association with heart dysfunction was found in those who had a history of hypertension and were taking beta blockers,” said lead author Andrew Davenport, M.D., and colleagues of the center of nephrology at UCL medical school. "However, because bioimpedance results can also be affected by malnutrition with loss of cell mass, NTproBNP may be elevated not only in patients with volume overload, but also those with malnutrition.”

NT-proBNP is a 76 amino acid N-terminal fragment of brain natriuretic peptide produced by overworked or damaged heart ventricles, accompanied by the loss of sodium through urine. Both BNP and NT-proBNP levels in the blood are used for screening and diagnosis of acute congestive heart failure (CHF) and may be useful in establishing prognosis as well, as both markers are typically higher in patients with worse outcome. The plasma concentrations of both BNP and NT-proBNP are also typically increased in patients with left ventricular dysfunction.

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