HEALTH / Common Procedures: Tests on the liver

MANY people know that the liver is the body's biggest organ (it weighs 2 1/2-4lbs) but few have much idea what it does - other than soak up the alcohol they drink. The liver is a chemical factory. It stores and processes the chemical breakdown products of the digestion of food and drink; it reprocesses the useful materials from damaged and worn-out cells; it manufactures amino acids and proteins (including the complex blood-clotting factors); and it detoxifies and eliminates the drugs we swallow - including alcohol.

Testing the health of the liver is, then, first a matter of testing how well it is carrying out some of these functions. Hospital laboratories have a standard package of 'liver function tests', which are done on a single sample of blood taken from a vein. These include measuring the blood concentrations of bilirubin (the yellow breakdown product from blood cells), proteins such as albumin, and some enzymes - the workhorses of the liver's chemical processing functions. A test of blood-clotting is usually included to check that enough clotting factors are being manufactured. If an infection seems possible, tests will be done for the main hepatitis viruses.

If all these tests give normal results, there is probably not much wrong with the liver - though it may function remarkably well when damaged because, like most body organs, it is designed to last a long time and has a lot of spare capacity. Further testing will be aimed at visualising the structure of the liver to identify disorders such as tumours and cysts.

Ultrasound scanning is relatively cheap, totally safe and causes no discomfort. Sometimes other scanning methods are used, including CT and magnetic resonance scans. Radionuclide scans require an injection into the bloodstream of radioactive chemicals. These chemicals are picked up by the liver cells, and the scan will show whether there are any regions of the liver working less efficiently than others.

More information may still be needed, especially if there seems to be a problem in the bile ducts connecting the liver to the gall bladder and the intestines. Scans show these quite well, but the best pictures come by passing an endoscope down the throat and into the intestines, so that dye can be injected directly into the main bile duct and X-rays then taken.

If the diagnosis still remains in doubt, or if there is some chronic disease such as hepatitis or cirrhosis affecting the whole liver, the ultimate test is the liver biopsy. This entails passing a hollow needle into the liver and removing some of it for examination using a microscope. There is a small risk of a little internal bleeding, but serious complications are very rare.