A doctor may order a number of different liver blood tests to check up on a patient's health. Liver blood tests include liver enzyme tests and liver function tests as well as tests for elevated levels of creatinine and alpha-fetoprotein (AFP). The tests are used to diagnose liver problems, including cirrhosis, cancer, and diseases such as hepatitis. Elevated blood proteins and liver enzymes found during a liver blood test may not necessarily mean that the liver is damaged, though.
When a person's liver is healthy, enzymes stay inside the liver's cells. If the organ is damaged, the enzymes escape from the cells and into a person's bloodstream. There are usually low levels of certain enzymes, such as alanine aminotransferase (ALT) or aspartate aminotransferase (AST), in the blood, and liver damage causes the levels to rise.
Common liver blood tests count the levels of ALT and AST in someone's blood. Ideally, a person should have a an ALT level between five and 40 units per liter of blood serum and an AST level between seven and 56 units per liter of blood serum. Higher levels can indicate liver damage or damage to another organ or muscle.
Other enzyme liver blood tests look for elevated levels of 5'nucleotidase (5'NT), gamma-glutamyl transferase (GGT), and alkaline phosphatase (ALP). Higher levels of these enzymes can point to cirrhosis or hepatitis C. In some cases, pregnant women and children may have elevated levels of ALP without suffering liver damage, as the enzyme is also produced by the placenta and bones.
Liver blood tests that examine the functioning of the organ look for low levels of certain blood proteins, such as albumin. The liver is responsible for producing albumin, a protein that prevents blood from leaking out of the vessels. Reduced levels of albumin signal disease in the liver or kidneys. Someone who doesn't eat enough protein or who is malnourished may also have low albumin levels.
Bilirubin is a waste product produced when red blood cells die. Usually, the liver helps the body excrete bilirubin by producing bile. If a person has jaundice, or yellowed skin, he most likely has excess bilirubin, which can be determined through a blood test.
An excessively damaged liver can impact the functioning of the kidneys. If a patient is on the wait list for a transplant, he may undergo a test of his creatinine levels to determine how damaged the organ is. The kidneys typically excrete creatinine, a waste product. Higher levels of creatinine suggest kidney and extensive liver damage.