The liver is a lobed organ located in the abdomen which is responsible for many excretory, synthetic and metabolic functions, some of which include:
- Detoxification of drugs and toxins.
- Conversion of sugars into glycogen.
- Manufactures bile, which aids in the digestion of fats.
- Storage of fat-soluble vitamins A, D, E, and K.
- Synthesising and storage of fats.
- Breaks down haemoglobin creating metabolites that are added to bile as pigment (bilirubin).
- Regulates chemicals in the blood.
- Blood clotting factors are produced by the liver.
- Converts ammonia into urea, which is excreted out of the body via the urine.
Enzymes are proteins which act as a catalyst for many biochemical processes. When the liver becomes damaged, enzyme levels in the blood can increase. These changes are picked up when your veterinarian performs a biochemical profile test on your cat. This is a test on the clear portion of the blood, painting an overall picture of how the organs are functioning.
Three particular enzymes will be elevated when the liver isn't functioning properly.
- Alanine transaminase (ALT) - This enzyme is found in high concentrations in the cat's liver and in smaller levels in the kidney, muscles, heart and pancreas. If liver cells are injured, inflamed or unable to function properly (due to fatty infiltration or blocked bile duct) increased levels of ALT will be released into the bloodstream.
- Aspartate transaminase (AST) - Found in many tissues and body fluids of the body including the liver, heart and skeletal cells, this enzyme is released by both the heart and liver when the cells of these organs become damaged.
- Alkaline phosphatase (ALP) - Produced by multiple organs including the liver, bones, intestines and kidneys, elevated blood levels can rise in liver disease or bile duct blockage or if there are bone conditions such as cancers. It may also be elevated if your cat has Cushing's syndrome.
Other tests which can suggest problems with the liver include:
Albumin (ALB): The most abundant plasma protein, albumin formed principally in the liver. It maintains osmotic pressure & as such is extremely important in regulating the exchange of water between the plasma & interstitial compartment (space between cells). Low levels of albumin in the blood can be a sign of liver disease.
Ammonia: A toxic byproduct of metabolism, the liver converts ammonia into urea, which is then excreted out of the body in the urine. High levels of ammonia build up in the bloodstream if the liver is unable to convert it to urea.
Bilirubin: This is a major breakdown product of red blood cells. When red blood cells wear out they are trapped in the spleen and destroyed, releasing bilirubin into the blood. This type of bilirubin is called unconjugated. This bilirubin is transported in the blood to the liver, where it is taken up and conjugated (joined with glucuronic acid). This conjugated form may either be stored in the liver cells or excreted into the bile. Bilirubin levels are increased in cats with liver disease, gallbladder disease or have excessive destruction of red blood cells (known as hemolysis).
Below is a table of normal biochemical profile values.
|Test||SI Units||Conventional (US Units)|
|Alanine aminotransferase (ALT)||5-130 u/L||5-130 u/L|
|Albumin (ALB)||24 - 41 g/L||2.4 - 4.1 g/dl|
|Alkaline phosphatase (ALP)||10-80 u/L||10-80 u/L|
|Amylase||500-1200 u/L||500-1200 u/L|
|Bilirubin-Total||0 - 6.84 u/L||0.0-0.5 mg/dL|
|Bilirubin-Direct||0 - 1.71 u/L||0.0 - 0.1 mg/dl|
|BUN||6.069 - 12.495 mmol/L||17 - 35 mg/dl|
|Calcium (CA)||1.875 - 2.7 mmol/L||7.5 - 10.8 mg/dl|
|Chloride||111 - 125 mmol/L||111 - 125 mEq/l|
|Cholesterol (CHOL)||1.092 - 4.42 mmol/L||42 - 170 mg/dl|
|Creatinine||70.72 - 159.12 µmol/L||0.8 - 1.8 mg/dl|
|Glucose||3.85 - 8.25 mmol/L||70 - 150 mg/dl|
|Magnesium||0.8-1.2 mmol/L||1.9-2.8 mg/dL|
|Phosphorous||1.0659 - 2.4225 mmol/L||3.3 - 7.5 mg/dl|
|Potassium||4.5 - 5.3 mmol/L||4.5 - 5.3 mEq/l|
|Sodium||147 - 156 mmol/L||147 - 156 mEq/l|