The liver is the chemical factory of the body: it stores and releases energy and minerals, makes bile and controls fat absorption. It also makes proteins, vitamins and hormones, regulates blood clotting, filters blood and breaks down waste products. A blood test can show problems with various of these processes, indicating what illness is causing the problems.
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Diagnosis and Tests
Reasons for testing liver function include:
- The liver is vital for existence and its failure is fatal.
- There are many processes that affect and are affected by the liver – we need to know which are working correctly.
- Many drugs affect the liver. It may be important to check the effect they are having on liver function.
- It can confirm or rule out conditions such as suspected liver disease, terminal liver failure, kidney disease, pancreatitis, damage due to alcohol (ab)use, glandular fever, vitamin B6 deficiency, heart disease, heart failure, myocardial infarction, liver trauma, muscle damage, metastases (certain cancers), healing fractures, Paget's liver disease, hyperparathyroidism, hepatic damage (e.g. hepatitis, toxins, cirrhosis), biliary obstruction, cholestasis, dehydration, diabetes insipidus, cystic fibrosis, leukemia, alcoholic cirrhosis, Hodgkin's disease, malnutrition, nephrotic syndrome, multiple myeloma, inflammatory bowel disease, collagen-vascular diseases.
A series of special blood tests can often determine whether or not the liver is functioning properly. These tests can also distinguish between acute and chronic liver disorders and between hepatitis and cholestasis. The most commonly performed blood tests include:
- Serum Bilirubin Test. Elevated levels of bilirubin often indicate an obstruction of bile flow or a defect in the processing of bile by the liver. Bilirubin is produced by the liver and is excreted in the bile.
- Serum Albumin Test. Below-normal levels of albumin, a protein made by the liver, are associated with many chronic liver disorders.
- Serum Alkaline Phosphatase Test. Elevated levels of alkaline phosphatase, an enzyme found in the bile, usually indicate an obstruction of bile flow, liver injury, or certain cancers.
- Serum Aminotransferases (transaminases). This enzyme is released from damaged liver cells.
- Prothrombin Time (PTT) Test. This test measures the time it takes for blood to clot. Blood clotting requires vitamin K and a protein made by the liver. Liver cell damage and bile flow obstruction can both interfere with proper blood clotting.
- Alanine Transaminase (ALT) Test. This enzyme is released from damaged liver cells.
- Aspartate Transaminase (AST) Test. This enzyme is released from damaged liver, heart, muscle, or brain cells.
- Gamma-glutamyl Transpeptidase Test. This enzyme is produced by the liver, pancreas, and kidneys and released into the blood when these organs are injured.
- Lactic Dehydrogenase Test. This enzyme is released when organs such as the liver, heart, lung, or brain are injured.
- 5-Nucleotidase Test. This enzyme is released by the liver when the liver is injured due to bile duct obstruction or impaired bile flow.
- Alpha-fetoprotein Test. This protein is produced by the fetal liver and testes, indicating hepatitis or cancer.
- Mitochondrial Antibodies Test. The presence of these antibodies can indicate primary biliary cirrhosis, chronic active hepatitis, and certain other autoimmune disorders.