The liver is the second largest organ in the human body (only the skin is bigger). The liver is also one of the most important organs, because it performs dozens of tasks that are critical to human health. Since most liver diseases cause only mild symptoms in the early stages, it's vital to detect these diseases early.

Basically, liver function tests, which are also routinely called "LFTs," assess the overall health and the anatomical integrity of liver. LFTs include measurements of albumin, various liver enzymes, bilirubin, cholesterol and total protein. All of these tests can be performed at the same time.

Liver function tests are generally divided into four categories.

1) Tests based on the detoxification and excretory functions. The serum bilirubin test is typical. Bilirubin is an orange-colored substance in bile produced by the breakdown of red blood cells. When bilirubin levels are high, a condition called jaundice occurs. Too much bilirubin is usually due to increased destruction of red blood cells (hemolysis) or because the liver can no longer remove bilirubin in a timely manner.

2) Tests that detect damage to the liver structure. There are a number of enzymes in the liver. Elevated liver enzymes indicate that there is damage to the liver cells, or that there is an obstruction to bile flow.

3) Tests based on bio-synthetic functions. These liver function tests typically include the serum albumin test and the serum globulin test.

Serum albumin is the main protein in blood plasma. A decrease in the serum albumin level may indicate chronic liver disease. Serum albumin can also be decreased in other conditions like kidney disorders and malnutrition.

The serum globulin test measures the three types of globulins (globulins contain most of the antibodies of the blood): alpha, beta and gamma. The liver synthesizes the first two and the cells of the immune system synthesize the gamma globulin. In liver disorders, the alpha and the beta globulin are decreased and the gamma globulin levels are significantly increased. The normal albumin globulin ratio is reversed.

4) Other tests might include ultrasonography and biopsy. Ultrasonography is done as the first test for diagnosing obstructive jaundice. It is also done in cases of gall stone disease and detecting lesions in the liver. Along with Doppler, it is used to assess the condition of the blood vessels.

Biopsy is done through the skin (sometimes with the ultrasonographic guidance) in cases of liver disease of uncertain cause. Biopsy can also uncover suspected cancers, enlarged liver and enlarged spleen.

In summary, liver function tests evaluate a wide range of normal tasks performed by the liver. But a reliable diagnosis also depends on a complete history and complete physical examination in addition to the test themselves.