What are elevated liver enzymes?
The liver is a lobed organ located in the abdomen which is responsible for many excretory, synthetic and metabolic functions.
- 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 hemoglobin creating metabolites that are added to bile as a pigment (bilirubin)
- Regulates chemicals in the blood
- The liver produces blood clotting factors
- Converts ammonia into urea, which the body excretes out of the body via the urine
Elevated liver enzymes occur when the cells of the liver are inflamed or damaged. Enzymes are proteins which act as a catalyst for many biochemical processes. An inflamed or damaged liver can leak enzymes into the bloodstream which are picked up on a biochemical profile, a test on the clear portion of the blood.
- Alanine transaminase (ALT) – This enzyme is found in high concentrations in the cat’s liver and 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 can also be elevated in cats with Cushing’s Syndrome.
Other liver tests
Albumin (ALB): The most abundant plasma protein, albumin formed principally in the liver. It maintains osmotic pressure and 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, excreted out of the body via 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 the spleen traps and destroy them, releasing bilirubin into the blood (unconjugated bilirubin). 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).