Liver Enzymes: Essential Biomarkers for Liver Health

The Biomarker Handbook is a curated series that seeks to provide readers with insights on each biomarker we cover in our blood test packages and its relation to our body.


As the body’s largest internal factory, the liver carries out a number of critical functions. It is thus no wonder that when the liver is damaged, it causes major illnesses or even death. The National Statistics in the UK rank liver disease as the fifth cause of mortality, while in the US it is recognised as the second most common cause of death related to the digestive system. Fortunately, most liver diseases are preventable since over 90% of them are due to alcohol, viral hepatitis, obesity, and other lifestyle causes.

What Are Liver Function Tests and Why Are They Important?

Liver function tests measure the level of different biomarkers such as proteins, biles, and enzymes that are produced or released by liver cells. The tests are performed as part of a routine checkup or when liver disease is suspected. The results assist the doctor to decide on the specific type of illness, assess how severe a disease is, or monitor response to treatments. For some diseases, the doctor may have to request for further testing, especially when the involvement of other organs is suspected.

The Specific Liver Enzyme Tests

The focus of this article is mainly on the liver enzyme tests. Enzymes are proteins that help to speed up a particular chemical reaction(s) in the body. Liver enzymes are normally found in the liver cells, but if there is damage to the liver, they leak and find their way to the bloodstream resulting in elevated liver enzymes on blood tests.

The most widely used enzyme tests include:

1. Alanine Aminotransferase (ALT)

Alanine aminotransferase, an enzyme primarily found in the liver, is involved in the critical step of converting food into energy. Usually, a low level (7 to 55U/L) of ALT is in blood serum, but a number of conditions can result in an elevation. ALT is elevated early during disease process, even before any symptoms and signs are apparent to you. ALT is also a liver specific enzyme, more so than AST, and is rarely elevated in conditions that are not related to liver cell damage.

Very high levels can be caused by acute hepatitis, an overdose of drugs such as paracetamol and liver cancer. In hepatitis, ALT levels go up to 10 times more than usual and can take 3 to 6 months to return to normal while in drug overdose, the levels may be 100 times higher.

When the ALT levels are slightly to moderately raised, they suggest longstanding infections such as chronic hepatitis, scarring of the liver (what is known as liver cirrhosis), obstruction of the ducts that carry bile from the liver to the gallbladder (bile ducts), alcohol abuse, or heart damage.

2. Aspartate Aminotransferase (AST)

The role of aspartate aminotransferase (AST) in the liver is primarily to help in the breakdown of proteins to provide energy. AST is mainly in the liver, heart and a lesser extent in kidneys and muscles. Normal levels of AST are usually between 8 and 40U/L.  In acute viral hepatitis, recent heart attack, burns, muscle damage, excessive physical activity and drug overdose, the levels may be ten times more than the average range.

Since AST is found in several organs, it can show organ damage that is not directly related to the liver. Therefore, elevated AST levels do not always point to liver damage and ALT is more specific to the liver than AST.

In most cases, the two tests, ALT and AST are concurrently used as part of liver function testing to determine the severity and likely cause of liver damage.

3. Gamma-glutamyl transpeptidase (GGT)

GGT enzyme is found in several organs but has the highest concentrations in the liver. Normal levels of CGT are 9 to 48U/L. Something unique about the CGT enzyme is that it is usually the first enzyme to rise when there is obstruction of the bile duct, a condition in which bile cannot flow from the liver to other parts of the digestive system. This therefore makes it the most sensitive liver biomarker for your doctor to detect bile duct obstruction problems.

High levels of GGT are also common in people with heavy consumption of alcohol as they are generally 2 to 3 times higher than in people who consume less than three drinks per day. GGT levels may also be elevated in other liver conditions, cardiovascular diseases and by certain drugs such as phenytoin.

4. ALP (alkaline phosphatase)

ALP enzyme is found in several organs, but the highest concentration is in the liver and bones. In the liver, most of it is on the edges of the bile ducts where it is needed for digestion of fats while in bones it is essential for the formation of bone cells. Elevated levels of ALP are thus commonly used in detecting blocked bile ducts and bone disorders that cause excessive bone formation. ALP levels are generally higher in children and adolescents because bones are still growing. The normal levels are about 45 to 115 U/L for an adult.

Signs and Symptoms to Watch Out For

Several conditions may contribute to abnormal liver enzyme levels ranging from hepatitis, drug poisoning or overdose with acetaminophen, alcoholic liver disease to heart failure.

Signs and symptoms that may accompany elevated liver enzymes are generalized and range from mild to moderate:

  • Jaundice (yellowing of the skin and the whites of the eyes)
  • Nausea and vomiting
  • Excessive bruising or bleeding
  • Swelling of the legs
  • Abdominal swelling
  • Dark-colored urine
  • Light-colored stools
  • Fatigue
  • Abdominal pain
  • Itching

When Should You See Your Doctor?

If you experience any of the above signs and symptoms or your tests results reveal that you have elevated liver enzymes, even if you have no symptoms, you should visit your doctor. Some conditions do not manifest any symptoms during early stages of the disease, and so, it is possible to have abnormal test results without symptoms. Any abnormal liver enzyme test warrants further investigation from your doctor to ascertain the cause, find other complications or associated illnesses, and treat accordingly.

Common Causes and Management of Elevated Liver Enzymes

  • Non-alcoholic fatty liver disease (NAFLD) accounts for more than more than 20% of the cases in adults. It is common in people with lifestyle diseases like diabetes, obesity, and hypertension. The good news is that it is almost entirely preventable by lifestyle modification, and if diagnosed is also reversible with lifestyle and dietary modifications. NAFLD is associated with elevated ALT and GGT, rather than AST. It is estimated that 70% of people with type 2 diabetes also have NAFLD.
  • Alcohol contributes 20 to 25% of the cases. Damage from alcohol can occur either from daily drinking or episodes of binge drinking. Absolute abstinence from alcohol is essential for management of alcoholic liver damage.
  • Medications like acetaminophen, statins, antibiotics, among others can cause severe damage if overdosing. Medications should always be taken as prescribed by physician or instructions from the manufacturer, and they should be locked out of reach of children and depressed or at risk people.
  • Viruses- hepatitis A, B and C viruses account for a significant number of liver problems. People who abuse drugs, share needles, tattooing instruments and come into contact with infected body fluids are at a higher risk and thus avoiding these situations is helpful. In addition, Hepatitis A can be spread through the fecal-oral route. So, proper food handling, using clean, safe water and maintaining hygiene is the mainstay of prevention. Highly effective vaccines exist for hepatitis A and B viruses.
  • High-cholesterol diets, and fad diets that promote rapid unhealthy weight loss increase the risk of formation of gallstones and bile duct obstruction. A clean, balanced diet is thus critical for liver function.

In summary, there are steps that you can take to improve liver function regardless of the cause or disease. They include:

  • Clean up your diet by eating plenty of whole foods that are low in fat and sugar. Eat plenty of liver-friendly foods such as broccoli, walnuts, garlic, brussels sprouts, asparagus, wheat grass, and turmeric.
  • Avoid fast foods, refined sugars in coffee and carbonated drinks, and refined carbohydrates (complex carbs are better source of energy than simple carbs)
  • Take medications as prescribed; keep them out of reach of those at risk (children, depressed)
  • Avoid excessive alcohol or stay away from it altogether
  • Exercise at least thrice every week, for 30 to 60 minutes
  • Lose weight the right way- by exercising and eating fewer calories per day. Rapid weight loss only worsens liver damage.

Alcohol and the Liver

It is difficult for someone to admit their heavy alcohol consumption, but when suspected, then a liver enzyme test will reveal elevated transaminases with the AST rising stronger than the ALT and GGT. Because of the potential reversible nature of alcoholic liver disease with sobriety, regular screening of the general population and early diagnosis are essential.

Many people do not think of the consequences of drinking other than the hangover that they experience the following day. The truth is that when we ingest alcohol, it goes directly into the bloodstream and travels throughout the body. The brain, liver, heart, kidneys, and the stomach are particularly vulnerable. Excessive alcohol consumption over the long term can cause liver disease, pancreatitis, kidney failure, heart failure, and brain damage. Moreover, alcohol damages the digestive system, degrading the body’s ability to process and absorb essential nutrients, especially the B and A vitamin families. At the same time, the high-calorie content of alcohol leads to unhealthy weight gain.

According to the American Association for the Study of Liver Diseases (AASLD) and the American College of Gastroenterology, alcohol remains a leading cause of liver disease globally. The WHO estimates that alcohol consumption accounts for about 20 to 50% of those cases. The liver is a robust organ, but then, it can only cope with a small amount of alcohol. The process of alcoholic liver damage takes an extended period of years or decades, and the unfortunate thing is that it does not cause any symptoms until severe damage has occurred. However the liver enzymes do indicate liver damage much earlier, and a good sign to stop drinking or significantly reduce your alcohol consumption. Liver damage if progressed to fibrosis and cirrhosis can be irreversible.

Alcoholic Liver Disease encompasses three main conditions that occur due to heavy consumption of alcohol; alcoholic fatty liver, alcoholic hepatitis, and cirrhosis. As one continues to drink heavily, liver damage progresses from fatty liver to permanent damage of cirrhosis. About 20% of alcoholics develop a fatty liver, which can be reversed if alcohol consumption is stopped, while 15% may get cirrhosis, which can cause death if not treated. Furthermore, alcohol worsens other liver diseases, making them more difficult to manage.

Once alcoholic liver damage has set in, the British Liver Trust recommends complete abstinence from alcohol. Although damage may already be done, recognizing the problem and consciously taking steps to solve it can help to achieve a full healthy life.

For prevention of liver damage, the Australian National Health and Medical Research Council recommends that both men and women should drink no more than two standard drinks per day. On a single occasion, drink no more than four standard drinks. A standard drink contains less than 10 grams of pure alcohol.

It is possible to drink at a level that is safe and still have fun. Here are a number of things that you can do to control your alcohol intake

  • Set realistic goals and stick to them
  • Do not drink on an empty stomach
  • Alternate non-alcoholic drinks and alcoholic drinks
  • Go for drinks with a lower alcoholic percentage
  • Avoid peer pressure situations that may tempt you to drink heavy
  • Dilute your alcohol drink with mineral water
  • Keep an honest journal to monitor your drinking.

Other Laboratory Tests to Consider

It is important to note that elevation of liver enzymes does not always equate to liver disease. Abnormal results mean that it may be a liver problem or not. For instance, elevation of AST may be seen in muscle damage or heart attack while ALP may be present in bone disorders.

The interpretation your lab results is best done by a health specialist who may suggest other tests which include:

  • Other liver function tests including albumin, total proteins, bilirubin and clotting time
  • Complete Blood Count (CBC) to detect infections
  • Kidney function and electrolyte tests to assess how well the kidneys are doing their job
  • Emergency and overdose drug testing to monitor drug overdose and toxicity
  • Blood alcohol level
  • Hepatitis screening
  • Radiology tests for liver and gallbladder to visualise the organ size, tumours or any obstruction
  • Liver biopsy, to collect a sample of liver tissue
  • Vitamin B12
  • Blood tests to screen for fatty liver, level of liver inflammation and fibrosis (such as LiverFast test)

 

Abnormal liver function tests act as a warning sign that something is wrong and should never be ignored.  If you have elevated enzymes or you suspect that something is wrong, address the matter with your doctor. Again, with or without liver damage, there are many things that you can do to improve your liver function. Put them into action, and your liver will thank you.


If you want to find out more about your liver enzymes and how to care for them, take a look at our lifestyle article here!

Interested in other biomarkers? Check out the rest of The Biomarker Handbook.

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