Comparing a point of care and an ELISA nt-proBNP tests for feline cardiac disease

Hanås S, Holst BS, Höglund K, Häggström J, Tidholm A, Ljungvall I. Effect of feline characteristics on plasma N-terminal- prohormone B-type natriuretic peptide concentration and comparison of a point-of-care test and an ELISA test. J Vet Intern Med. 2020 Mar 22.

Cardiac disease is a common condition in domestic cats. Unlikely dogs, a large proportion of cats with heart disease have no heart murmur or other physical signs in the subclinical phase. Definitive diagnose of cardiac issues involved ultrasonography, which may be expensive and limited in availability. Diagnosis of pre-clinical heart disease and active congestive heart failure (CHF) are such challenges in general practice, and so biomarkers of heart disease have been developed. The most common of these is nt-proBNP, which may be used to detect increased stretch to the ventricular myocardium. This test is available both as a dichotomous point of care (PoC) test, as well as a quantitative laboratory test. Despite its widespread use, there is little data on the breed and individual characteristics that influence BNP status in cats.

The purpose of this paper was to determine if there is a correlation between BNP and breed, sex, age, weight, or body condition score (BCS); if it can be used to differentiate cats with hypertrophic cardiomyopathy (HCM) from normal cats; and if there is a correlation between PoC and reference lab results. Client owned cats were recruited from a private veterinary hospital over a 3-year period.

Cats were between 1 and 14 years of age, healthy or with preclinical or stable clinical HCM. Cats were excluded for hypertension, hyperthyroidism, chronic kidney disease (CKD), or diabetes mellitus. They were also excluded for decompensated heart disease or cardiac disorders other than HCM. All cats received blood pressure measurement, echocardiography, CBC and basic serum chemistries. Quantitative BNP analysis was sent to a reference lab, and in house PoC BNP testing.

One hundred eighteen apparently healthy cats were recruited to the study, of which 18 were excluded for the above criteria. 48 cats with murmurs or previously diagnosed HCM were recruited, of which 9 were excluded. This left 100 health control cats, 32 cats with HCM and no LA enlargement, and 7 cats with HCM and left atrial (LA) enlargement.

The median nt-proBNP concentration was higher in male cats than females (49 pmol/L vs <24 pmol/L). BNP was higher in cats with systolic anterior motion (SAM) than in those who did not. nt-proBNP trended upwards with increased LVFWd (left ventricular free wall in diastole). These were the only findings that were maintained over multivariate analysis; breed, weight, age, and BCS were not associated with BNP.

The PoC BNP assay had a sensitivity of 72-74% and a specificity of 95-98%. The sensitivity became 100% and sensitivity of 95-98% when considering only cats with LA enlargement. The ELISA and PoC tests did not have significantly different results.

This paper had a large number of wide-ranging goals and suffered from a fairly low sample size to achieve those goals. It also excluded cats with comorbidities, which represent a significant portion of cats with HCM.

This study suggests that male cats have a higher np-proBNP than female cats, but that there is no other variation associated with biologic parameters. It also suggests that laboratory and PoC tests have similar sensitivity and specificity. (MRK)

See Also

Machen MC, Oyama MA, Gordon SG, et al. Multi-centered investigation of a point-of-care NT-proBNP ELISA assay to detect moderate to severe occult (pre-clinical) feline heart disease in cats referred for cardiac evaluation. J Vet Cardiol. 2014;16:245-255.