The liver is the largest organ in the abdominal cavity. It is located in the right upper quadrant of the abdomen. It has several functions that include removing toxins from the body, creating new proteins, and contributing to digestive function. It is also essential to regulate glucose metabolism and our red blood cell levels and quality.
Liver function tests are important exams doctors can do when evaluating one of these functions or all of them. In most cases, when we talk about liver function tests, we refer to aspartate transaminase (AST) and alanine transaminase (ALT). They are essential liver enzymes, but not the only ones. There is also gamma-glutamyl transferase (GGT) and other substances produced or metabolized by the liver, including albumin or serum bilirubin.
Their levels are not only important to figure out if there is a liver injury or not. Actually, the pattern of alteration is also essential to determine the diagnosis.
Before going through the types of liver function tests, we should know that “liver function tests” are actually a misnomer because these exams only indirectly show how the liver is working. They do not measure directly how the liver works or the proportion of the liver that remains functional. Still, a careful examination of these tests gives doctors enough information to understand what happens in the body and what parts or functions of the liver are compromised.
Let us review three types of liver function tests and why they are important to diagnose liver-related disease.
Hepatocellular function tests
These tests are perhaps the most common and include the liver enzymes AST and ALT. They are both hepatocellular injury markers. In other words, they are increased due to hepatic injury, when hepatocytes break and release their contents into the intercellular space and the blood.
AST and ALT’s function is transferring a chemical group known as an amino group from aspartic acid to ketoglutaric acid. Out of these two, the most important is ALT because this enzyme can only be found in the liver, and it is a concrete marker for hepatocellular injury. On the contrary, AST is also found in heart muscle, skeletal muscle, the kidneys, and other organs. Thus, we can find an elevation of AST with a perfectly healthy liver.
