Abnormal Liver Blood Tests
What are liver blood tests?
Liver blood tests, sometimes referred to as liver function tests or LFTs, do not refer to one single value but to a series of results. Although they are called liver function tests, they do not truly reflect the function of the liver (see below).
The liver may be broadly divided into two parts: the liver cells and the bile duct system. Liver blood tests can be divided in the same way. They generally reflect problems in the respective areas, although with some overlap.
ALT (alanine aminotransferase) and AST (aspartate aminotransferase) are two enzymes in liver cells that are measured to give information on liver cell activity.
GGT (gamma glutamyl transferase) and ALP (alkaline phosphatase) belong to the bile duct system.
Bilirubin comes from the breakdown of red blood cells. It is metabolised (digested) by the liver cells and then released into the bile duct system. Because bilirubin is involved in both areas, a high bilirubin may reflect injury to either the liver cells or bile duct system.
What can you tell from liver blood tests?
Liver blood tests are useful to screen for inflammation or disease activity in the liver.
Sudden increases in liver blood tests can reflect numerous causes- ranging from medications, herbal remedies, supplements, viral infections to alcohol excess, weight gain, and weight loss.
Generally, elevations in ALT and AST reflect problems in the liver cells such as viral hepatitis such as hepatitis A/B/C/D/E, or autoimmune hepatitis, as well as liver injury from alcohol, fat or medications.
High GGT and ALP usually reflect problems in the bile duct system such as autoimmune causes such as primary biliary cholangitis, primary sclerosing cholangitis, or blockage due to gallstones or biliary/pancreatic cancers.
Oftentimes the picture is mixed, with elevations in one or more enzymes from both the liver cell and biliary systems; this may be seen with alcohol, NAFLD/NASH, or drug induced liver injury.
What can you not tell from liver blood tests?
Liver blood tests are not good at saying how much scarring (fibrosis or cirrhosis) is present in the liver. Sometimes they can be used to try to predict this (e.g. FIB4 score). However, using scans like Fibroscan or sometimes a liver biopsy is generally more appropriate.
Liver blood tests in advanced liver disease/cirrhosis
Standard liver blood tests, as outlined above, do not always tell the whole story for patients with severe liver damage or cirrhosis. Often, many of them may even appear to be normal.
Instead, the main indicators of liver function include levels of bilirubin, albumin, prothrombin time/INR, and platelet count; kidney function (sodium and creatinine) are also extremely important indicators of the severity of liver disease.
A series of tests can be combined into a score which is used as an estimate of how well the liver is working. The MELD score or MELD Na score are two of the most useful scoring systems. These scores combine sodium (an electrolyte in the blood), creatinine (a marker of kidney and muscle activity), bilirubin, and INR (a marker of blood clotting ability – your liver makes some clotting factors) in a special calculation.
Platelets levels (another blood clotting ability test) are also useful to check in the context of cirrhosis. Some patients with cirrhosis develop portal hypertension (a build up of pressure in the blood supply to the liver). Low platelets in the blood are a sign of portal hypertension. Portal hypertension may cause the spleen to become bigger and platelets to deposit there as a result. Since portal hypertension leads to varices (dilated veins in the gullet), low platelets (less than 150) may act as a trigger to search for these using endoscopy.