NT-proBNP in cats and dogs

What it shows

Heart muscle cells store a precursor hormone, proBNP. When the heart wall is stretched or strained, proBNP is released and split into active BNP and an inactive fragment, NT-proBNP. The fragment lasts longer in the blood, so it is the one labs measure. The more the heart is under strain, the higher the value tends to be.

A form can show it in several ways:

• NT-proBNP without a species — the general line, used when the lab did not say whose test it was.
• NT-proBNP (canine) and NT-proBNP (feline) — species-specific tests with their own interpretation thresholds. A dog’s and a cat’s numbers are not compared with each other.
• NT-proBNP SNAP — a quick in-clinic test for cats that gives no number, only “normal” or “abnormal”: the sample spot is compared with a reference spot, and a spot as dark as or darker than the reference counts as abnormal.

Higher than reference — what it may be a sign of

• Heart disease with stretch of the heart muscle — cardiomyopathy in cats, valve disease or dilated cardiomyopathy in dogs. A high result is a reason for further tests, most of all an echocardiogram.
• Heart failure as the cause of breathing problems — in an animal with laboured breathing, a markedly raised value makes a heart cause more likely than a lung one.
• Reduced kidney function — NT-proBNP is cleared mainly by the kidneys, so kidney disease or dehydration with azotemia can raise it without heart disease.
• In cats: hyperthyroidism and high blood pressure — both can raise the value; it is not assumed to be the thyroid alone, and the result is read together with T4 and blood pressure.

Lower than reference

A low or “normal” result means there is no evidence of increased strain on the heart muscle at the moment, so clinically significant heart disease is unlikely right now. A normal SNAP result is described as helping to rule out moderate to severe heart disease. Heart disease can still develop later, so for the SNAP test in cats the manufacturer suggests repeating it next year.

Look at together with

• Heart ultrasound (echocardiogram), chest X-rays, ECG and blood pressure — the tests that actually show the heart.
• Creatinine, SDMA and urine specific gravity — to judge whether the kidneys are part of the reason for a high value.
• Total T4 — in cats, to look for hyperthyroidism.

Units and conversion

Quantitative tests report NT-proBNP in pmol/L (on Russian forms пмоль/л); no conversion is needed. The SNAP test has no unit at all — the app stores its result as text.

Reference range

The reference range is on your lab’s form, and labs usually print interpretation comments next to it. IDEXX, which makes the Cardiopet proBNP test, publishes its own thresholds. For cats without signs, below 100 pmol/L means significant heart disease is unlikely, and 100 or more calls for further tests; for cats with breathing problems, from 270 pmol/L the signs are likely due to heart failure. A normal SNAP result corresponds to below 150 pmol/L, and an abnormal one is followed by the quantitative test. For dogs with a heart murmur the line is 900 pmol/L; for dogs with signs, the IDEXX criteria named 900–1,800 a grey zone, and a later IDEXX update raised the upper cut-off for dogs with breathing problems to 2,500 pmol/L: above it heart failure is likely. A rise of about 60% between two tests is, by the same guidance, a reason for a closer look at the heart.

Cats and dogs

Sources

1. IDEXX — Interpretive Criteria for the Feline Cardiopet proBNP Test
2. IDEXX — Interpretive Criteria for the Canine Cardiopet proBNP Test
3. IDEXX — Cardiopet proBNP Test: diagnostic update (What is NT-proBNP?)
4. IDEXX — SNAP Feline proBNP Test: diagnostic update
5. IDEXX — Catalyst proBNP Test
6. Cornell Feline Health Center — Cardiomyopathy