The Use of ProBNP as a Screening Test for Occult Heart Disease in Cats Prior to Anesthesia

3 min read

Introduction

Pre-anesthetic screening in cats is essential to minimize anesthetic risk, particularly since occult (hidden) cardiomyopathy is common and often asymptomatic. One increasingly used tool is the measurement of N-terminal pro-B-type natriuretic peptide (NT-proBNP) or proBNP, a biomarker released from cardiac muscle in response to wall stress. This essay discusses the utility, strengths, limitations, and strategic role of proBNP testing in routine anesthetic cases for cats, considering the Bayesian principle and the base rate fallacy.

Utility and Accuracy of ProBNP Testing

NT-proBNP is a useful biomarker for detecting occult heart disease in cats, especially before anesthesia. It is particularly valuable for:

Detection of subclinical heart disease in cats prior to the development of overt clinical signs.
Differentiation between cardiac and non-cardiac causes of respiratory distress.
Selection of cats requiring further echocardiographic evaluation prior to anesthesia^[1][2][3].

Test accuracy varies by population:

In referral settings and symptomatic cats, NT-proBNP has a sensitivity of around 86–90% and specificity of 85–91% for distinguishing cats with occult cardiomyopathy from healthy controls^[2][4].
In general practice and apparently healthy cats, recent studies show the sensitivity drops to 43–71% (lower in the absence of a murmur), while specificity remains high (92–96%)^[5][6][7].
Positive predictive value (PPV) in high-risk populations is about 90.7%, and negative predictive value (NPV) is about 86.7%, but these change with disease prevalence^[1].
Point-of-care (POC) tests may underperform quantitative laboratory assays, especially in low-risk populations.

Pros and Cons

Pros	Cons
Non-invasive, rapid screening tool	Lower sensitivity in low-prevalence populations
High specificity—few false positives if abnormal	False negatives possible, especially in early/mild disease
Helps prioritize cats for echocardiography	Cannot stage severity or suggest specific therapy
Useful in cats with murmurs or arrhythmias	Day-to-day biological variation; lab error can yield false results
Can guide anesthesia decisions, reducing risk	Cost considerations for routine use

The Bayesian Principle and the Base Rate Fallacy

A Bayesian approach underscores that a test’s predictive value depends not only on its intrinsic accuracy but also on the prevalence (base rate) of disease in the tested population. This is the essence of the base rate fallacy: clinicians often overestimate the likelihood of disease when a test is positive, especially if the prevalence is low.

Example in Context:

Suppose only 10% of cats in a population have occult cardiomyopathy. If the NT-proBNP test has 90% sensitivity and 85% specificity^[4], a positive result does NOT mean there’s a 90% chance the cat has heart disease. Applying Bayes’ theorem:

For every 100 cats: 10 truly have disease, 90 do not.
True positives: 9 cats (90% of 10).
False positives: 13.5 cats (15% of 90).
Total positives: 22.5 cats, of which only 9 are true positives.
Therefore, the post-test probability (PPV) is 9/22.5 ≈ 40%, not 90%.

This demonstrates that positive results in low-prevalence populations have much lower predictive value—the classic base rate fallacy in action^[8][9][10].

Recommendations for Use in Routine Anesthesia

NT-proBNP testing is most justified in “at-risk” cats:
- Middle-aged and older cats (from about 7–10 years^[4][11])
- Cats with murmurs, arrhythmias, or breed predispositions (Maine Coon, Ragdoll, Sphinx, etc.)^[6][12]
- Cats with suggestive history or abnormal physical exam^[12]
In apparently healthy, young cats (under ~7 years, no risk factors), indiscriminate screening may yield more false positives than true positives, causing unnecessary stress and expense.
Routine use is not recommended in all cats prior to anesthesia. Instead, use as an adjunct in cats with risk factors or abnormal findings^[13][4][6].

Guidelines by Age and Signalment

Under 7 years, Healthy, No Murmur: Test not routinely recommended.
7 years and older, especially >10 years: Consider NT-proBNP if possible, particularly for breeds at risk, cats with new murmurs, arrhythmias, or unknown cardiac history.
Any age, murmur/gallop/arrhythmia or risk breed: NT-proBNP screening is indicated prior to anesthesia^[6][12][11].
Abnormal NT-proBNP: Proceed to echocardiography if possible before anesthesia; defer elective procedures in favor of further workup if practical^[13][4].

Conclusion

NT-proBNP is an important screening tool for occult cardiomyopathy in cats, especially in at-risk populations and those with abnormal auscultatory findings prior to anesthesia. However, its limitations—including lower sensitivity when used broadly—mandate judicious use. Clinicians should respect the Bayesian principle: even a highly specific and sensitive test cannot overcome the constraints of low disease prevalence. The test should be reserved for cats where the pre-test probability is increased by age, breed, or clinical findings.

In summary, routine use is best reserved for older cats or those with clinical risk factors. Positive results must be interpreted in context, ideally followed with echocardiography. Owner counseling on the strengths and limitations of the test is essential to avoid misinterpretation and unnecessary treatment or anxiety^[1][2][4].

Updated on August 2, 2025

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The Use of ProBNP as a Screening Test for Occult Heart Disease in Cats Prior to Anesthesia