Circulating Natriuretic Peptides Concentrations in Cats with Respiratory Distress
Cats in respiratory distress (RD) can represent a significant diagnostic challenge. The ability to distinguish cardiac from non-cardiac causes of RD is a vital initial step to achieving an accurate diagnosis and appropriate treatment. It is often not possible to do this on the basis of history and physical examination and the compromised state of cats with severe RD often limits diagnostic evaluation. Human and canine studies have shown circulating B-type natriuretic peptide concentration to be an accurate predictor of congestive heart failure (CHF) enabling patients with CHF to be differentiated from those with non-cardiac causes of RD (RDNC). In contrast to dogs and humans, relatively little is known about the utility of natriuretic peptide testing in cats. It has been established that circulating NT-proANP and particularly NT-proBNP concentrations measured by ELISA identified cats with heart disease and heart failure. The study aim was to determine if circulating natriuretic peptide (NP) concentration could distinguish cats with RDNC from those with CHF.
The study recruited 91 cats from 1 university teaching hospital and 2 private practices. Serum natriuretic peptide concentrations were measured in 41 cats with RDNC (diseases included asthma, neoplasia, pyothorax, pneumonia, pleural effusion, bronchitis, rhinitis, nasopharyngeal stenosis, nasopharyngeal polyp) and compared to cats with asymptomatic heart disease (AsymHD n=17) and cats with RD due to CHF (RDCHF n=33) using sandwich enzyme immunoassays. The diagnoses in the cats with heart disease included hypertrophic cardiomyopathy, hypertrophic obstructive cardiomyopathy or both (n=36); restrictive cardiomyopathy (n=10); dilated cardiomyopathy (n=1); mitral dysplasia (n=1); double-chambered right ventricle (n=1); and idiopathic third degree atrioventricular block (n=1). The ability of circulating NP concentrations to distinguish cats with RDNC from those with RDCHF was explored using receiver operator curve (ROC) analysis. The RDCHF group had higher median NT-proANP and NT-proBNP concentrations (1690 and 523 fmol/ml respectively) than the RDNC group (614 and 45 f/mol/ml p< 0.05 and p<0.05 respectively). The area under the curve was 0.88 and 0.96 for the ROC analysis of the diagnostic accuracy of NT-proANP and NT-proBNP concentrations to discriminate RDCHF from RDNC cats. An optimum cut-off concentration of 986 fmol/ml for NT-proANP and 220 fmol/ml for NT-proBNP accurately discriminated RDNC from RCCHF cats with a sensitivity and specificity of 93.8% and 80.3% and 93.9% and 87.8% respectively.
Serum NP concentrations were different in cats with CHF compared with those with respiratory distress of non-cardiogenic origin. Evaluation of circulating NP concentrations may be helpful in the initial approach to cats presenting with respiratory distress.