A liver blood test, also known as a liver function test or a liver function blood test, is a routine test that your doctor may perform to determine whether or not your liver is functioning properly. More specifically, you might have to have a liver blood test to diagnose liver disease, to see if your liver is damaged, to monitor the progression of a disease you’ve already been diagnosed with, or to see if your treatment to help treat liver damage is being successful. Liver function blood tests are often done to see if an excess intake of alcohol is causing long-term liver damage.
This article on liver function blood tests is by Kathryn Senior, a freelance journalist who writes health, medical, biological, and pharmaceutical articles for national and international journals, newsletters and web sites.
What does your liver do?
Your liver is known as your body’s ‘chemical factory’ because it produces many substances that are important to your body’s normal functioning. Some examples include bile that helps with digestion, and blood proteins that help with blood clotting. In addition to producing these substances, your liver is also responsible for several other key functions in your body, including:
- Breaking down toxins that are harmful to the body
- Storing certain nutrients
- Converting fat to energy
What does a liver blood test look for?
A liver function blood test checks for a variety of substances in your blood that may indicate symptoms of liver disease or liver dysfunction problems. These substances include:
- Liver enzymes: In a healthy body, liver enzymes are found only in the liver tissue itself. However, if your liver cells are damaged or dying, these enzymes leak into your bloodstream. It is a good indication that something might be wrong if you have high levels of liver enzymes in your liver blood test. Liver damage has several possible causes, including a blockage in your liver or bile duct, viral or auto-immune hepatitis, inflammation of the liver from certain medications, excessive alcohol intake, a fatty build up in your liver cells, a tumour in your liver, or even heart failure.
- Proteins: Since your liver produces several proteins that help with your body’s normal functioning, liver blood tests also measure the levels of these proteins in your bloodstream. Proteins that the liver blood test checks for include antibodies, which help to fight off infections, albumin, which maintains the amount of blood in your arteries, and prothrombin, which helps to clot your blood. You may have liver or kidney disease if your protein levels are abnormally high or low in your liver blood test. Liver malfunction can also occur as a result of blood cancer, bleeding disorders, malnutrition (specifically a lack of vitamin K), or a reaction from certain blood-thinning medications.
- Bilirubin: This is a yellow fluid produced in the liver when old red blood cells are broken down. Normally, your liver is responsible for removing it from the blood so when it appears in a liver blood test this means there is a problem. The presence of bilirubin in your blood also causes jaundice, which shows itself physically as a yellow discolouration of the skin, eye membranes and other mucous membranes, and is a common reason for a doctor to request a liver blood test. Liver diseases such as cirrhosis or viral hepatitis, or a blocked bile duct can also lead to abnormal bilirubin levels.
How is the test done?
A liver function blood test involves taking blood. A nurse or doctor will insert a needle into a vein in your arm and withdraw blood, which is then sent off for testing at a laboratory. You may be asked to go back to your doctor during the next couple of weeks to get your results. You don’t have to prepare for the liver blood test, though your doctor may ask you not to eat anything for a few hours before the sample is taken.
What can’t a liver function blood test show?
It’s important to realise that since there may be many causes of liver dysfunction, a liver blood test is not the only test that will be performed in order for your doctor to make an accurate diagnosis. Besides the blood test, liver malfunction may be diagnosed through other tests and by finding out about your medical history. For example, if in the results of the blood test, liver cells are shown to be damaged, your doctor may ask for more liver blood tests to look for specific disorders that may have caused the damage, such as cirrhosis or hepatitis.
What if your tests are borderline?
Sometimes some of the proteins and enzymes measured by a liver function blood test are only slightly raised. The levels are not dangerously high, but they need to be monitored. In this case, you may be asked to return to your doctor or to the hospital for a repeat liver function blood test after six months. It is common for you to get advice to cut down on alcohol consumption during that time, if that is thought to be a contributory factor.