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Clinical Evaluation of Heart Disease
Hematologic Evaluation
1. Can blood work diagnose heart failure?
There is no blood test that can definitively determine the existence of heart failure. However, the detection of certain circulating hormones or enzymes, so-called biomarkers, may provide strong evidence in support of heart failure or even heart disease. See below.
2. What cardiac abnormalities can be diagnosed by blood work?
  • A number of findings can support a reduced cardiac output:
    • evidence of reduced renal perfusion (reduced GFR)
      • increase BUN/creatinine or reduced urinary output
    • depressed venous oxygen tension (venous pO2) levels
    • elevated lactate levels
    • reduced serum sodium
  • Muscle enzyme elevations (CPK, SGOT, LDH) are almost uniformly of no value in detecting heart disease of domestic animals; isoenzymes may be of more value to detect myocardial necrosis.
  • Circulating cardiac troponin I (cTnI) is a general marker of cardiac myocyte injury. It is elevated in a number of canine and feline cardiac diseases, including dilated and hypertrophic cardiomyopathies, subaortic stenosis, and chronic mitral valve disease, but also in other diseases that may secondarily cause myocardial injury. In dilated cardiomyopathy, cTnI levels may relate to prognosis. Several human cTnI assays have been validated in dogs and cats.
  • Plasma norepinephrine is elevated in all causes of heart failure and the level relates to prognosis.
  • Plasma aldosterone and angiotensin II are elevated in heart failure.
  • Atrial Natriuretic Peptide (ANP) and Brain Natriuretic Peptide (BNP) are elevated in humans, cats, and dogs with heart failure of various causes. For more information on BNP see the next question.
  • Use of certain cardiac drugs, like digoxin, necessitates monitoring drug levels.
  • Can detect electrolyte imbalances that may contribute to heart disease.
  • Can detect acid-base imbalance that may contribute to heart disease.
  • Can detect thyroid imbalance that may contribute to heart disease.
  • Can suggest infection in cases of infective heart disease.
  • Can assay serum taurine levels or carnitine levels, which may be important in dilated cardiomyopathy.
  • Can assay for Lyme's Disease, which can cause myocarditis and conduction abnormalities.
  • Can assay for evidence of heartworm disease
3. Why is BNP a potentially useful test in veterinary medicine?
BNP, specifically NT-proBNP, has been demonstrated in human medicine to have an extremely important role in the diagnosis and management of heart disease and heart failure:
  • It is used to discriminate between a primary respiratory disorder and CHF in patients with respiratory signs.
  • It predicts prognosis in patients with CHF.
  • It may reflect response to treatment, and so help guide therapy.
  • It may be useful to identify asymptomatic (occult) cardiac disease prior to the onset of symptoms.

Review of BNP:

  • Released from the heart due to:
    • Atrial or ventricular stretch/dilation
    • High hydrostatic pressure
    • Hypertrophy
    • Ischemia, neurohormones
  • Effect of BNP:
    • Causes natriuresis and vasodilation
    • Counteracts the RAAS
  • Metabolism of BNP:
    • Produced as a prohormone
    • Cleaved by a neutral endopeptidase into 2 moieties
      • C-BNP
        • The biologically active moiety
        • Unstable with a very short half life
      • NT-proBNP
        • Biologically inactive
        • Stable with a long half life
        • ELISA assay used to detect
  • The current assay available in veterinary medicine is called Cardiopet proBNP through IDEXX labs.

    Use of the NT-proBNP test in Cats:

    • Why might there be a place for this test in cats?
      • Many cats with heart disease are asymptomatic
      • Radiographic findings in cats with heart disease can be variable and inconclusive
      • Heart murmurs or gallops in cats with heart disease may be intermittent, difficult to detect, or not present. Furthermore, innocent or physiologic murmurs are common in cats.
      • Although echocardiography is usually definitive, it may not be available or may be expensive
    • Role for NT-proBNP in Cats:
      • Identify heart disease in high-risk populations that are asymptomatic (to determine if they are "likely" or "unlikely" to have heart disease)
        • Older cats
        • Cats with either a heart murmur or a gallop
        • Breeds at high risk such as the Maine Coon
        • Recommendations:
          • NT-proBNP > 50 pmol/l is highly likely to indicate underlying heart disease.
      • Sensitivity and specificity are reported to be 90% and 85% respectively, however this may apply mostly to the detection of severe disease. Therefore recognize that there is the potential for false negatives, particularly in the case of mild to moderate disease. False positives are also possible.
        • For cases that are too fragile for diagnostics or that can't afford echocardiography.
        • Radiographs are always indicated in the presence of respiratory signs, however findings can sometimes be inconclusive.
        • Recommendations:
          • NT-proBNP > 270 pmol/l is highly likely to indicate the presence of CHF
        • Cats with NT-proBNP between 50-270 pmol/l likely have heart disease but may or may not have CHF.

    Use of the NT-proBNP test in Dogs:

    • Where might there be a place for this test in dogs?
      • To identify dogs with asymptomatic (occult) DCM
      • To differentiate between primary respiratory disease and CHF as the cause for respiratory clinical signs
      • To assess prognosis and guide therapy
    • To identify dogs with asymptomatic heart disease:
      • Recommendations:
        • NT-proBNP > 900 pmol/l is likely to indicate the presence of heart disease
        • Recognize again that both false positives and false negatives will occur.
      • Dogs with DCM tend to have higher values than dogs with CMVI
      • The more advanced the heart disease the higher the levels of NT-proBNP
      • NT-proBNP > 680 pmol/l were associated with radiographic evidence of cardiomegaly (VHS > 11.5)
    • To differentiate between primary respiratory disease and CHF as the cause for respiratory clinical signs:
      • Recommendations:
        • NT-proBNP > 2700 pmol/l is highly likely to indicate the presence of CHF in patients with evidence of heart disease.
        • Dogs with NT-proBNP between 900-2700 pmol/l likely have heart disease but may or may not have CHF.


      • Prerenal and renal azotemia may cause significant elevations in NT-proBNP therefore levels must be interpreted with caution in patients with elevated urea and creatinine.
      • Pulmonary artery hypertension (without left sided heart disease) also elevates NT-proBNP levels, and may be present in patients with primary respiratory disease.
      • Prolonged shipping or inappropriate storage will result in a reduction (degradation) of NT-proBNP.
      • Day to day variability likely exists. Week to week variability in normal dogs ranged between 37 to 51%.