Aim: To assess the correlation between the amino-terminal pro-hormone brain natriuretic peptide (NT-proBNP) concentration in blood and urine during a period when actively adjusting the treatment of heart failure (HF).
Methods: Plasma and urine analyses of NT-proBNP were compared in 51 patients on admission to and discharge from a nurse-led outpatient clinic where HF treatment was optimized. The median time between the two measurements was 42 days. Correlations were analyzed using linear regression, where R(2) is the degree of variability in the plasma NT-proBNP concentration that can be accounted for by the urinary NT-proBNP.
Results: There was a statistically significant linear relationship between the urine and plasma concentrations of NT-proBNP on both occasions, but R(2) varied greatly depending on how the data were presented. The correlation between the raw data showed an R(2) of only 30%, and it almost doubled upon logarithm transformation, which shows that the variability (error) was concentration-dependent. Correction of the urinary NT-proBNP for urinary creatinine further increased R(2) for the logarithm-transformed correlation to 68% on admission and 76% on discharge. The highest R(2) (77%) was obtained when the relative changes in urinary NT-proBNP/creatinine between admission and discharge were compared with the corresponding relative changes in the plasma concentration. The sensitivity and specificity of the urine in indicating plasma concentration changes > 10% were 82% and 86%, respectively.
Conclusion: Relative changes in plasma NT-proBNP could be reliably estimated from urine samples during a period of optimization of HF treatment.
Keywords: Heart failure; brain; natriuretic peptide; patient monitoring; urinary NT-proBNP.