Cardiac Biomarker: NT-proBNP
By Dr. Justin Thomason
The natriuretic peptides (NP) (atrial, ANP and ventricular, BNP) are synthesized and stored in the myocytes of the atria and ventricles. The synthesis of the NP is increased whenever the atria or ventricles are stretched. Secretion of NP into the blood increases proportionately with the degree of chamber dilation or increased intra-cavitary pressure. Because of this, NP can be utilized in the diagnosis of cardiac diseases. NT-proBNP is the most common NP evaluated in clinical cardiology.
Currently, the value of NT-proBNP in veterinary medicine is that the levels can be measured in a plasma sample. NT-proBNP assay is valuable, especially in private practice when echocardiography is not available or not available in a timely fashion. If heart disease is suspected then a NT-pro-BNP assay is indicated. If the plasma concentration is normal, then heart enlargement is absent or minimal. If the level is markedly elevated, additional diagnostics (thoracic radiographs and/or echocardiogram) would be indicated. As an example, suppose you are presented a cat with a heart murmur. Given that physiologic heart murmurs are common in cats, NT-proBNP can be used to distinguish between potential pathologic murmurs (indication for echocardiography) or the common physiologic murmurs (DRVO-dynamic right ventricular outflow tract obstruction). The NT-proBNP has a great negative predictive value (sensitive test). Therefore, a normal result would indicate that a physiologic murmur is most likely and echocardiography is not indicated. However, if the result is positive, a more specific test (echocardiography) would be indicated to better assess for structural heart disease (hypertrophic cardiomyopathy in cats). Due to NT-proBNP being eliminated by the kidneys, do not evaluate if azotemia is present (with kidney disease the NT-proBNP will always be elevated). As time passes, our knowledge and the utility of the NP assays will no doubt increase significantly.
Justin Thomason, DVM (SAIM; Cardiology) is a board certified cardiologist in the Veterinary Health Center at Kansas State University in the College of Veterinary Medicine.