The liver is located in the right upper portion of the abdominal cavity just beneath the right side of the rib cage and it has many vital functions, for example, detoxification of blood, metabolizing (processing) medications and nutrients, production of important clotting factor and other important proteins, processing of waste products of hemoglobin.
Liver blood tests can assess liver functions or liver injury. A simple blood test can determine the presence of certain liver enzymes (proteins which help to speed up routine and necessary chemical reactions in the body) in the blood because, under normal circumstances, these enzymes reside within the cells of the liver.
When the liver is injured for any reason, these enzymes are spilled into the blood stream raising their levels and signaling liver disease. The focus is mainly on the most common liver enzymes, the enzyme aspartate aminotransferase (AST – also known as serum glutamic oxaloacetic transaminase (SGOT)) and alanine aminotransferase (ALT – also known as serum glutamic pyruvic transaminase (SGPT)).
AST (SGOT) is normally found in a variety of tissues including liver, heart, muscle, kidney, and brain. It is released into the serum when any one of these tissues is damaged, so it is not a highly specific indicator of liver injury as it can occur from other injured tissues.
ALT (SGPT) is, by contrast, normally found largely in the liver, so it serves as a fairly specific indicator of liver status.
The normal range of values for AST (SGOT) is from 5 to 40 units per liter of serum (the liquid part of the blood).
The normal range of values for ALT (SGPT) is from 7 to 56 units per liter of serum.
The blood tests that truly reflect the liver function are:
- Coagulation panel (prothrombin time or PT, and the international normalized ratio or INR): The tests measure blood's ability for normal clotting and prevention of bleeding and bruising.
- Albumin level (hypoalbuminemia): Protein albumin is produced only in the liver, and if its levels are lower than normal it can be suggestive of the chronic liver disease.
- Bilirubin: The byproduct of the routine destruction of red blood cells and their elevation can suggest liver dysfunction.
- Platelet count: Low platelet count (thrombocytopenia) has many causes, one of which can be advanced liver disease.
Abnormal liver tests may be detected in the blood in a variety of liver conditions.
Most common are fatty liver (caused by alcohol abuse, diabetes mellitus and obesity) and chronic hepatitis B and hepatitis C. Also, some medications can cause mild to moderate increase in the liver enzymes (pain relief medications, anti-seizure medications, antibiotics, cholesterol lowering drugs, cardiovascular drugs, and some other drugs). Within weeks to months after stopping the medications, the enzymes usually normalize.
Less common causes of abnormal liver enzymes include hemochromatosis (iron overload), Wilson's disease (inherited disorder with excessive accumulation of copper in diverse tissues including the liver and the brain), alpha-1-antitrypsin deficiency (lack of a glycoprotein (carbohydrate-protein complex) called alpha-1-antitrypsin lead to chronic lung disease (emphysema) and liver disease), celiac disease (allergy to gluten and develops gas, bloating, diarrhea, and in advanced cases malnutrition), Crohn's disease and ulcerative colitis (chronic inflammation of the intestines), and autoimmune hepatitis (the body's own antibodies and defense systems attacking the liver).
Rarely, abnormal liver enzymes can be a sign of cancer in the liver. Cancer arising from liver cells is called hepatocellular carcinoma or hepatoma. Cancers spreading to the liver from other organs (such as colon, pancreas, stomach, etc) are called metastatic malignancies (to the liver).