New studies show uses for NT-proBNP
This biomarker increases as myocardial stretch increases. An increase also can occur with renal disease. The role this assay will play in small animals is still being investigated. Several research abstracts presented at the 2011 American College of Veterinary Internal Medicine (ACVIM) Forum in Denver dealt with this topic.
Evaluating cats with respiratory difficultiesNT-proBNP concentrations have been found to be useful in differentiating cardiac disease from respiratory tract disease in cats evaluated at referral institutions.1 Using a cutoff of 265 pmol/L, the assay was 90 percent sensitive and 88 percent specific for differentiating between cats with congestive heart failure (CHF) and those with dyspnea and respiratory disease. These results are good, since it means that with a value of more than 265 pmol/L, only one out of 10 cats with CHF would be missed, and only one out of 10 cats with this value is going to have respiratory disease as the underlying cause for dyspnea.
It's assumed this assay's greatest value is for practicing veterinarians. Specialists can use various advanced diagnostic tests and their experience to guide a diagnosis, so the NT-proBNP assay will play less of a role in diagnosis.
A multicenter study evaluated this issue by having 47 general practice veterinarians look at cases using an online survey.2 The veterinarians, who had been in practice between five and 10 years, were asked to diagnose either CHF or primary respiratory disease and to rank how confident (1 = lowest, 10 = highest) they were of their diagnosis. Information provided included history, physical examination findings, radiographic and electrocardiographic examinations and routine blood work. Half the cats had CHF and half had primary respiratory disease. Initially, a correct diagnosis was made in 67.4 percent of the cases with a confidence level of 6. After the initial input, the veterinarians were given the NT-proBNP result, which increased their diagnostic accuracy to 85.5 percent and their confidence level to 8.
This study is similar to others that have shown the use of NT-proBNP can increase diagnostic accuracy when trying to assess patients with respiratory distress. However, unlike other studies, it looks at a more real-life scenario in that general practitioners were doing the evaluations in conjunction with routine testing (e.g., history, physical examination, radiography, electrocardiography).
Certainly this study shows the blood test can aid in accurate diagnosis in cats with respiratory distress, as well as increase veterinarians' confidence levels when making a diagnosis. The only downside at this time is that the NT-proBNP assay is a send-out test, so in the true emergency patient, it's of limited value. Hopefully, this assay will become available for in-house use in the near future, in which case it will allow veterinarians to make more accurate diagnoses and feel more confident in their ability to differentiate respiratory disease from cardiac disease as a cause of respiratory distress.