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Liver Disease in Pets

overview

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What is liver disease?

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Often the first sign of liver disease is an elevation of two key enzymes on a general blood test, known as ALT and ALP. ALT is released when liver cells are damaged, while ALP increases if bile flow through the liver is slower than normal. Elevation in these enzymes suggests something may be affecting the liver but doesn't tell us whether these changes are significant or not. It is very common to find elevated liver enzymes on routine blood tests, such as pre-anaesthetic screens or when monitoring drug use. We can't assume there is serious liver disease from these enzyme levels alone, however, there are several additional tests that can be performed to give us more information.

diagnosis

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What tests are used to diagnose liver disease in pets?

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Bile Acid Stimulation Test

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Known as a BAST, this is a specific blood test involving two samples taken two hours apart, with a meal in between. The test looks at how the liver responds to the meal and is a good indicator of how the liver is functioning. Liver function is important for metabolism of drugs, including those used during anaesthesia. If the liver is not functioning normally, the BAST result will be increased. There are many possible causes of liver dysfunction, so an abnormal BAST result alone does not give us a diagnosis.

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Ultrasound

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An ultrasound scan lets us assess the structure of the liver. Significant structural changes are easily seen, such as masses on the liver. Diffuse disease can show as abnormalities in the texture of the liver but does not always cause visible changes. Ultrasound also allows us to examine the gall bladder and other abdominal organs. Most animals will allow ultrasound to be performed either awake or under light sedation. It requires the fur to be clipped over the abdomen but is not a painful procedure.

Liver function and structural changes do not always correlate - either can cause an increase in ALP and ALT so often both a BAST and ultrasound examination are advised.

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Liver function and structural changes do not always correlate - either can cause an increase in ALP and ALT so often both a BAST and ultrasound examination are advised.

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Further blood tests

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Several systemic conditions can cause a secondary increase in liver enzymes, especially endocrine diseases such as Cushing's disease or diabetes. Additional blood tests may be required to rule these conditions in or out.

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Urinalysis

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Liver disease can impair the kidneys ability to concentrate urine, however this is only seen in very progressed disease. If the urine is very dilute this may suggest another underlying condition and can help direct investigations.

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Biopsy

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Ultimately, the only way to know exactly what is happening in the liver is with a tissue biopsy. Sometimes this can be obtained via ultrasound, but more commonly a surgical biopsy is needed. Surgery allows the liver to be examined visually and biopsies can be taken from specific areas. Although this isn't a high-risk surgery, it is advisable to measure the blood's ability to clot beforehand. In some clinics, liver biopsies can be performed laparoscopically (keyhole) which is less invasive and may be preferable for unwell animals.

outlook

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What is the outlook for pets with liver disease?

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Not all pets with increased ALP or ALT have significant liver disease. Some changes are transient, and caused by an acute insult such as trauma, ingestion of something mildly toxic, or medication. The liver has an amazing ability to regenerate, so often small injuries will resolve in time. A variant of ALP can be released by bone, intestine, or due to steroids - these can contribute to raised ALP on a blood test, though ALT will often be normal. If your vet suspects there is not significant liver disease present, they may suggest repeating the blood test in 3-6 weeks to see if the enzymes have lowered, with or without a course of medication to support the liver.