Background: Amino-terminal probrain natriuretic peptide (NT-proBNP) has been proposed as a useful biomarker for heart disease in dogs. In humans, decreased glomerular filtration rate (GFR) increases NT-proBNP.Objective: To investigate whether decreased GFR as indicated by plasma creatinine concentration is associated with increased NT-proBNP in dogs without heart disease.Animals: Four groups of dogs: healthy (n 5 39), azotemic (n 5 36), heart disease (n 5 37), and congestive heart failure (CHF) (n 5 7) presented to 2 teaching hospitals.Methods: Prospective observational cohort study. Plasma creatinine concentration and NT-proBNP were measured in every dog. Nonparametric tests were used to compare the differences among groups. The median and actual results for each group were compared with the manufacturer's recommended and previously published suggestions for cut-off values for diagnosis of heart disease.Results: Median (range) plasma creatinine concentration was 1.47 (1.06-1.70), 4.36 (1.74-15.6), 1.22 (0.69-1.91), and 1.45 (0.63-1.64) mg/dL and median (range) NT-proBNP was 118 (2-673), 556 (37-1,819), 929 (212-5,658), and 3,144 (432-5,500) pmol/L for the healthy, azotemic, heart disease, and CHF groups, respectively. Pair-wise comparison indicated a significant difference among all groups for NT-proBNP (P .049). Plasma creatinine concentration was significantly higher in the azotemic group compared with other groups (P o .001) but there was no significant among other groups. Application of 3 recommended cut-off values led to misclassification of dogs with azotemia as having heart disease.Conclusions: Azotemia results in NT-proBNP being increased to concentrations reported as diagnostic of heart disease or heart failure in dogs. Care should be employed when interpreting the results of NT-proBNP in patients with known or possible increased plasma creatinine concentration.

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