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Heart failure in dogs: NT-proBNP, blood work and stages

Most dogs with heart failure have a leaky mitral valve or, in large breeds, a weak heart muscle. The diagnosis rests on the heart exam, X-rays and an ultrasound of the heart. Blood tests add a heart marker, NT-proBNP, and keep watch on the kidneys and electrolytes once treatment starts.

Written by the AI DiagAnimals editorial teamReviewed by the AI DiagAnimals TeamUpdated Our editorial policy

The essentials

Heart failure is the last step of a heart disease that often starts years earlier with a murmur. Vets use the ACVIM stages A to D. NT-proBNP rises when the heart is stretched: a normal value in a coughing or breathless dog makes heart failure unlikely, but it does not replace an ultrasound of the heart. Once treatment starts, creatinine, BUN and electrolytes are rechecked, and at home you count the sleeping breathing rate.

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The two main causes

About 10% of dogs seen in general practice have heart disease. Myxomatous mitral valve disease (MMVD), a slow thickening of the valve between the left chambers, is the most common: about 75% of heart disease cases in North America [1]. It mostly affects small dogs under 20 kg, such as Cavalier King Charles Spaniels, Dachshunds and Poodles, and up to 85% of small-breed dogs show the valve lesion by 13 years of age [1]. Most dogs have a murmur for years before any sign of heart failure [1].

Dilated cardiomyopathy (DCM) is the most common heart disease of large-breed dogs. It can start with irregular beats or with a heart muscle that pumps weakly [2]. It is inherited in Doberman Pinschers, where it affects 58% of dogs [3].

The ACVIM stages

Stages from the 2019 ACVIM consensus on mitral valve disease [1]. A dog stays in stage C even when the signs are controlled.
StageWhat it meansUsual tests
AAt risk, no heart disease found yet (for example, a Cavalier King Charles Spaniel without a murmur)Yearly listening to the heart in at-risk small breeds
B1Murmur, no signs, heart not enlarged or only mildlyX-rays, blood pressure, ultrasound; recheck in 6–12 months
B2Murmur, no signs, but the left heart is clearly enlargedUltrasound measurements (or X-rays) confirm the enlargement
CCurrent or past signs of heart failureX-rays, ultrasound, kidney values and electrolytes
DHeart failure that no longer responds to standard treatmentClose follow-up of kidney values and electrolytes

Typical signs of stage C are fast breathing, restlessness, breathing difficulty or cough [1]. Many of these dogs also have airway disease, so a murmur in a coughing dog does not prove heart failure [1].

NT-proBNP: the heart stretch marker

NT-proBNP is released when the heart walls are stretched. In one study, a value above 445 pmol/L separated dogs with heart disease from healthy dogs with 83% sensitivity and 90% specificity [4]. In dogs with breathing signs, values above 1,158 pmol/L [5] or above 2,447 pmol/L with a newer test [6] pointed to heart failure rather than a lung problem. Values also climb with the ACVIM stage [6].

Limits matter. A normal or near-normal NT-proBNP in a dog with cough or breathlessness strongly suggests the heart is not the cause, but no single value proves heart failure [1]. Healthy Labradors and Newfoundlands have about three times the NT-proBNP of Dachshunds [7], and dogs with kidney disease and a normal heart had higher values than healthy dogs (617 vs 261 pmol/L) [8]. An ultrasound of the heart is still needed to find the cause of a murmur [1].

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
NT-proBNP N-terminal pro-B-type natriuretic peptide2600pmol/L< 445H
  1. Abbreviation NT-proBNP, sometimes listed as “Cardio BNP” or “proBNP”. It is often a separate test, not part of the routine chemistry.
  2. Result 2600 pmol/L in this illustrative line: well above the cut-offs used in studies [4, 6].
  3. Unit pmol/L: picomoles per liter. Compare results only within the same test and laboratory.
  4. Laboratory interval An illustrative cut-off based on one study [4]; each laboratory sets its own, and breed and kidney function shift values [7, 8].
  5. Flag H: above the interval. It shows heart stretch, not the cause. Your vet reads it with the ultrasound, X-rays and kidney values.

What the rest of the blood work shows

Basic tests recommended in dogs with heart failure [1].
TestWhy it is checked
Cardiac troponin I (cTnI)Measures heart muscle injury, not its cause. Higher values are linked to a worse outlook in mitral valve disease and cardiomyopathies [9].
Creatinine and BUNKidney function. Checked before treatment and 3–14 days after starting a diuretic or an ACE inhibitor; a creatinine rise of 30% or more raises concern for kidney injury [1].
ElectrolytesSodium, potassium and chloride. Low chloride is the most common change in acute heart failure (about 1 dog or cat in 4) [11].
PCV and total proteinPart of the minimum database in heart failure, with urine specific gravity [1].

Troponin also rises in many non-heart diseases, such as pancreatitis, pyometra, parvovirus or heartworm, and should be read with caution when the kidneys are failing [9]. Ask about a heartworm test where this parasite is present.

Heart, kidneys and treatment: why the rechecks

The heart and the kidneys depend on each other. A failing heart can reduce blood flow to the kidneys or congest them, and heart medicines such as diuretics and ACE inhibitors can also affect kidney function [10]. Older dogs with heart disease may have kidney disease of their own as well [10].

For this reason, vets adjust treatment using repeated checks of hydration, kidney values, electrolytes, blood pressure, body weight and urine output [10]. Potassium is watched closely, especially when spironolactone is combined with an ACE inhibitor or when the kidneys are weak [10]. Low potassium seems more common with torsemide, and high potassium is rare [1]. A poor appetite raises the risk of kidney values climbing on treatment [1].

How heart failure is confirmed and followed at home

  • Chest X-rays: show whether there is fluid in the lungs (congestive heart failure) [10].
  • Echocardiography (heart ultrasound): identifies the cause of the murmur and measures heart size and function [1, 10].
  • Blood pressure: recommended for every dog with mitral valve disease and in kidney disease [1, 10].
  • Holter (24-hour ECG) and ultrasound for DCM: yearly from 3 years of age in Dobermans; troponin I and NT-proBNP are extra tests when these are not available [3]. In Dobermans, NT-proBNP above 400 pmol/L detected DCM with 81% sensitivity and 75% specificity [14].
  • Sleeping breathing rate at home: a rise above your dog’s usual rate is the best early warning of decompensation [1]. Dogs with heart disease but no heart failure usually breathe fewer than 25 times a minute while asleep [12], and most dogs with well-controlled heart failure stay under 30 [13].

Related articles

See also the CBC for dogs and the urinalysis.

En français : insuffisance cardiaque du chien.

Questions to ask your veterinarian

  1. Which ACVIM stage is my dog in, and when should we recheck?
  2. Would an NT-proBNP or troponin test help in my dog’s case?
  3. Should we do an ultrasound of the heart and chest X-rays?
  4. When should creatinine, BUN and electrolytes be rechecked after a medication change?
  5. What sleeping breathing rate should make me call you?
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Frequently asked questions

Can a blood test detect heart disease in dogs?

NT-proBNP can suggest it: above 445 pmol/L it separated dogs with heart disease from healthy dogs with 83% sensitivity in one study [4]. It cannot replace an ultrasound of the heart, and breed and kidney disease change the values [1, 7, 8].

What are the four stages of heart failure in dogs?

The ACVIM stages: A (at risk), B (murmur without signs, split into B1 and B2 by heart size), C (current or past heart failure) and D (heart failure that no longer responds to standard treatment) [1].

What is cardiomyopathy?

A disease of the heart muscle. Dilated cardiomyopathy is the most common heart disease of large-breed dogs and can start with irregular beats or weak pumping [2]. It is inherited in Dobermans [3].

What is a normal sleeping breathing rate for a dog with heart disease?

Dogs with heart disease but no heart failure usually breathe fewer than 25 times a minute while asleep [12]. Most dogs whose heart failure is well controlled stay under 30 [13].

Why are kidney values checked on heart medication?

Heart failure and some heart medicines can affect the kidneys, so creatinine, BUN and electrolytes are checked 3–14 days after starting certain drugs and after changes [1, 10].

Sources

  1. Keene BW et al. ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. J Vet Intern Med. 2019;33(3):1127-1140. doi.org/10.1111/jvim.15488
  2. Wess G. Screening for dilated cardiomyopathy in dogs. J Vet Cardiol. 2022;40:51-68. doi.org/10.1016/j.jvc.2021.09.004
  3. Wess G et al. European Society of Veterinary Cardiology screening guidelines for dilated cardiomyopathy in Doberman Pinschers. J Vet Cardiol. 2017;19(5):405-415. doi.org/10.1016/j.jvc.2017.08.006
  4. Oyama MA et al. Clinical utility of serum N-terminal pro-B-type natriuretic peptide concentration for identifying cardiac disease in dogs and assessing disease severity. J Am Vet Med Assoc. 2008;232(10):1496-1503. doi.org/10.2460/javma.232.10.1496
  5. Oyama MA et al. Assessment of serum N-terminal pro-B-type natriuretic peptide concentration for differentiation of congestive heart failure from primary respiratory tract disease as the cause of respiratory signs in dogs. J Am Vet Med Assoc. 2009;235(11):1319-1325. doi.org/10.2460/javma.235.11.1319
  6. Fox PR et al. Relationship of plasma N-terminal pro-brain natriuretic peptide concentrations to heart failure classification and cause of respiratory distress in dogs using a 2nd generation ELISA assay. J Vet Intern Med. 2015;29(1):171-179. doi.org/10.1111/jvim.12472
  7. Sjöstrand K et al. Breed differences in natriuretic peptides in healthy dogs. J Vet Intern Med. 2014;28(2):451-457. doi.org/10.1111/jvim.12310
  8. Schmidt MK et al. Effect of azotemia on serum N-terminal proBNP concentration in dogs with normal cardiac function: a pilot study. J Vet Cardiol. 2009;11 Suppl 1:S81-S86. doi.org/10.1016/j.jvc.2009.02.001
  9. Langhorn R, Willesen JL. Cardiac troponins in dogs and cats. J Vet Intern Med. 2016;30(1):36-50. doi.org/10.1111/jvim.13801
  10. Pouchelon JL et al. Cardiovascular-renal axis disorders in the domestic dog and cat: a veterinary consensus statement. J Small Anim Pract. 2015;56(9):537-552. doi.org/10.1111/jsap.12387
  11. Roche-Catholy M et al. Clinical relevance of serum electrolytes in dogs and cats with acute heart failure: a retrospective study. J Vet Intern Med. 2021;35(4):1652-1662. doi.org/10.1111/jvim.16187
  12. Ohad DG et al. Sleeping and resting respiratory rates in dogs with subclinical heart disease. J Am Vet Med Assoc. 2013;243(6):839-843. doi.org/10.2460/javma.243.6.839
  13. Porciello F et al. Sleeping and resting respiratory rates in dogs and cats with medically-controlled left-sided congestive heart failure. Vet J. 2016;207:164-168. doi.org/10.1016/j.tvjl.2015.08.017
  14. Wess G et al. Evaluation of N-terminal pro-B-type natriuretic peptide as a diagnostic marker of various stages of cardiomyopathy in Doberman Pinschers. Am J Vet Res. 2011;72(5):642-649. doi.org/10.2460/ajvr.72.5.642

Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.

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