Bilirubin
Bilirubin is a yellow-orange pigment that results from the breakdown of haemoglobin, the red blood pigment that transports oxygen. Bilirubin is processed in the liver and excreted with bile into the intestine, where it gives feces its brown color. If the bilirubin level in the blood is too high, this can indicate various health problems in dogs.
What are the causes of high bilirubin in dogs?
There are several possible causes of high bilirubin levels in dogs, which can be divided into two categories: prehepatic and posthepatic.
Prehepatic means that the problem lies before the liver, i.e. in the bloodstream or bone marrow. In this case, too much bilirubin is produced because the red blood cells are broken down too quickly. This can be triggered by various factors, such as
- Autoimmune diseases in which the immune system attacks its own red blood cells
- Toxins that damage the red blood cells, such as onions, garlic, paracetamol or zinc
- Infectious diseases that affect the red blood cells, such as babesiosis or leishmaniasis
- Hereditary disorders that affect the structure or function of red blood cells, such as pyruvate kinase deficiency or spherocytosis
Posthepatic means that the problem is located after the liver, i.e. in the bile ducts or in the intestine. In this case, too little bilirubin is excreted because there is a backlog or blockage. This can be caused by various factors, such as
- Liver diseases that affect the function or structure of the liver, such as cirrhosis, hepatitis or liver tumors
- Bile duct diseases that impede the patency or flow of bile, such as gallstones, bile duct inflammation or bile duct tumors
- Intestinal diseases that interfere with the absorption or transportation of bilirubin, such as intestinal inflammation, intestinal infection or intestinal obstruction
How is a high bilirubin level diagnosed in dogs?
In order to diagnose a high bilirubin level in dogs, the vet must carry out a blood test. This measures the total bilirubin level, which consists of two forms: unconjugated (indirect) and conjugated (direct) bilirubin.
Unconjugated bilirubin is bound to albumin and is insoluble in water. It is produced from the breakdown of hemoglobin in the macrophages. The liver absorbs it and combines it with glucuronic acid, making it water-soluble.
Conjugated bilirubin is water-soluble and is excreted into the intestine with bile. It is also the form of bilirubin that appears in the urine (which is not normal in dogs, except in very concentrated urine).
Measuring the total bilirubin and bilirubin split (direct and indirect bilirubin) in the blood can help the vet determine the cause of the problem. For example, an increase in unconjugated bilirubin may indicate increased production of bilirubin due to hemolytic anemia. An increase in conjugated bilirubin may indicate decreased excretion of bilirubin due to cholestasis.
The veterinarian may also perform other tests to check liver function. These include:
- Alanine aminotransferase (ALT): an enzyme found in the liver that is released into the blood when liver damage occurs
- Gamma-glutamyltransferase (GGT): An enzyme that is found in the bile ducts and is released into the blood when the bile ducts are damaged
- Alkaline phosphatase (ALP) : An enzyme found in various tissues, but mainly in the liver and bones. It can be elevated in various diseases, such as liver cirrhosis, gallstones or bone diseases
- Aspartate aminotransferase (AST): An enzyme found in various organs, but mainly in the liver and heart. It can be elevated in various diseases, such as liver cirrhosis, heart attack or muscle injuries
The vet may also perform a urinalysis to look for bilirubin in the urine. This is an indication of cholestasis or an increased concentration of conjugated bilirubin in the blood.
To find the exact cause of a high bilirubin level in dogs, the vet may order further tests, such as:
- X-rays or ultrasound to assess the structure and size of the liver and bile ducts
- Biopsy or aspiration to take a tissue sample from the liver or bile ducts and examine it under a microscope
- Bacteriologic culture or PCR to look for infectious agents in the liver, bile ducts or intestines
- Serological tests or immunofluorescence to look for antibodies against specific pathogens or autoantigens
How is high bilirubin treated in dogs?
Treatment of high bilirubin in dogs depends on the underlying cause. The goal is to eliminate or control the cause and relieve the symptoms.
Treatment may include the following:
- Antibiotics, antiparasitics or antifungals to fight infections
- Immunosuppressants or corticosteroids to treat autoimmune diseases
- Fluid therapy or blood transfusions to correct dehydration or anemia
- Choleretics or cholekinetics to promote bile production or flow
- Cholesterol-lowering medication or diet to prevent gallstones
- Hepatoprotectors or antioxidants to support liver function
- Painkillers or anti-inflammatories to relieve pain or inflammation
- Surgery or endoscopy to remove blockages or tumors
How to prevent high bilirubin in dogs?
High bilirubin in dogs cannot always be prevented, especially if it is caused by hereditary or unpredictable factors. However, there are some measures that can be taken to reduce the risk or improve the prognosis. These include:
- Regular veterinary examinations and blood tests to identify and treat potential problems early on
- A balanced and high-quality diet that meets the dog's needs and does not contain harmful substances
- Adequate hydration and exercise to improve blood circulation
The authors assume that a veterinarian should be consulted if an animal is ill and that medication should only be taken after consultation with a doctor or pharmacist. Only an individual examination can lead to a diagnosis and treatment decision.
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