The Utility of NT-proBNP to Differentiate Cardiac and Respiratory Causes of Dyspnea in Cats
In clinical practice it is necessary to differentiate cardiac and respiratory causes of dyspnea, as treatment of cardiac and respiratory cases is very different. This differentiation however is often not easy and expensive, but important for further decisions on diagnostics and therapy. Measurement of B-type Natriuretic Peptide concentrations (BNP) is helpful in distinguishing cardiac from non cardiac cause of dyspnea in dogs and humans. Previous canine studies have shown elevated BNP and NT-proBNP in dogs with congestive heart failure. BNP is synthesized as a prohormone proBNP, secreted into the blood stream and cleaved into N-Terminal ProBNP (Nt-proBNP) and BNP. Nt-proBNP has no physiological activity, but is more stable than BNP and therefore easier to measure.
The purpose of this prospective study was to evaluate the utility of Nt-proBNP to differentiate cardiac and respiratory causes of dyspnea in cats. A healthy control group was used to obtain reference values for Nt-proBNP.
Nt-proBNP was measured in plasma samples from 74 cats using an ELISA antibody assay (VETSIGN Feline CardioSCREEN Nt-proBNP, Guildhay Ltd, UK). The cats were classified according to echocardiography and thoracic x-rays into one of the following groups: clinical healthy (control) group (n = 33, mean age 4.6 years), cats with dyspnea due to respiratory causes (n = 21, mean age 8.7 years) and dyspnea due to cardiac causes (n = 20, mean age 8.7 years). Cardiac causes were decompensated hypertrophic cardiomyopathy (n = 14), restrictive cardiomyopathy (n = 4) and DCM (n = 2).
There was no significant difference (p < 0.001) between the control group (mean Nt-proBNP 120 +/- 107 pmol/l) and the respiratory group (mean Nt-proBNP 170 +/- 143 pmol/l). Nt-proBNP values of cats with dyspnea due to cardiac causes were significantly (p < 0.001) higher than in the other groups (mean Nt-proBNP 686 +/- 368 pmol/l). Using a cut-off value of 277 pmol/l Nt-proBNP had a sensitivity of 95.0 % and a specificity of 84.6 % for the differentiation between cardiac and respiratory causes of dyspnea in cats.
In conclusion, this feline ELISA Nt-proBNP assay was helpful in the diagnosis of CHF in cats and had a very high sensitivity and good specificity to differentiate between cardiac and respiratory causes of dyspnea.