Understanding Liver Enzymes and Signs of Liver Dysfunction

Liver enzymes are proteins in your liver that speed up chemical reactions. If your liver is damaged, blood tests will show abnormally high levels of these enzymes circulating in your bloodstream.

Determining which enzyme is elevated—or if multiple enzymes are elevated—can help determine causes of liver disease such as hepatitis, cirrhosis, liver cancer, and liver failure.

Types of Liver Enzymes

Common types of liver enzymes that may be detected in blood tests include:

• Alanine aminotransferase (ALT): Also known as serum glutamate-pyruvate transaminase (SGPT), it breaks down amino acids and supports the production of energy.
• Aspartate aminotransferase (AST): Also known as serum glutamic-oxaloacetic transaminase (SGOT), this enzyme plays a key role in metabolizing amino acids. 
• Alkaline phosphatase (ALP): Although the complete function of ALP is unclear, it plays a role in developing hard tissue and maintaining bone health.
• Gamma-glutamyl transferase (GGT): This enzyme helps metabolize glutathione, an antioxidant that plays a role in immunity and cell repair. 
• Lactate dehydrogenase (LDH): Present in almost all your body tissues, LDH helps cells make energy.

These enzymes are found in other areas of the body, not just the liver. To determine if elevated levels are directly related to liver damage, other tests need to be done.

Why Liver Enzyme Levels Are Tested

A comprehensive panel of tests known as a liver function test (LFT) will check for ALT and AST and may also check for other enzymes. Your healthcare provider may order an LFT for a number of reasons:

• If you have symptoms of liver disease, including jaundice (yellowing of the skin or eyes), dark urine, pale stools, nausea, vomiting, and fatigue
• To monitor the progression of a liver disease
• To determine when drug treatments should be started
• To check your response to treatment

High levels of the enzymes in the blood are reliable markers for liver disease.

Normal Levels

Liver enzymes are measured in international units per liter (U/L). The normal range of values (meaning the values between which levels are normal) are:

• ALT: Between 4 and 36 U/L
• AST: Between 8 and 33 U/L
• ALP: Between 44 and 147 U/L 
• GGT: Between 5 and 40 U/L
• LDH: Between 125 and 220 U/L
  

The high end of the reference range is referred to as the upper limit of normal (ULN).

Abnormal Levels

Elevated levels of certain liver enzymes can indicate liver inflammation, injury, or disease. 

AST Levels

A test of AST levels can help diagnose liver problems. Elevated levels can indicate:

• Hepatitis
• Cirrhosis
• Mononucleosis
• Heart disease
• Pancreatitis
• Too much iron in the body (hemochromatosis)
• Deep burns
• Seizures
• Alcohol use
• Use of other drugs toxic to the liver
• Recent surgery

Low ranges are not a concern.

ALT Levels

Elevated ALT may indicate a range of liver problems, including

• Hepatitis
• Liver cancer
• Lack of blood flow to the liver

Certain medications can also raise ALT levels in the blood.

Low levels of ALT in the blood could indicate a vitamin B6 deficiency or chronic kidney disease.

ALP Levels

ALP is present in the bones as well as the liver. Elevated levels are associated with:

• Cirrhosis
• Hepatitis
• Mononucleosis
• Blockage in bile ducts

Lower levels of ALP in the body may be caused by nutritional deficiencies.

GGT Levels

GGT levels are often checked to assess alcohol abuse or liver damage. It may indicate one of the following underlying issues:

• Hepatitis
• Cirrhosis
• Pancreatitis
• Diabetes
• Heart failure
• Alcohol use disorder (AUD)

Lower levels of GGT are not a sign of a health issue.

LDH Levels

Results of LDH levels are usually used to check for tissue damage. If LDH levels are higher than normal, you may have tissue damage in some area of the body. However, your blood test may also indicate high levels following intense exercise or after taking medications such as aspirin.

Lower than normal levels usually do not indicate a problem. Your tests may show low levels if you have taken large quantities of vitamin C or E.

What Can Affect the Results?

High or liver enzyme results are not always due to a health problem. Certain factors can cause a temporary increase or decrease in levels, such as:

• Recent heavy alcohol use
• Extreme physical activity
• Pregnancy
• Recent cocaine use (which is hepatotoxic)
• Recent fasting or extreme weight loss

Obesity, sex, and age can also influence ALT or AST levels, meaning that what is considered "normal" overall may need to be adjusted if you are overweight or underweight, male or female, or older or younger. Labs will generally take these factors into account.

How to Lower High Levels

You can treat high enzymes in the liver. Methods of lowering liver enzyme levels vary depending on what is causing the elevation. Common treatments for liver disorders such as nonalcoholic fatty liver disease include:

• Following a low-fat, nutrient-rich diet
• Avoiding alcohol and toxic drugs
• Losing weight
• Controlling cholesterol
• Control blood sugar
• Protect yourself from sexually transmitted infections

It takes time to regain balance. You may not be able to lower liver enzymes quickly, but with the right changes, it can happen.

Summary

Liver enzymes play an important role in the body. If you show signs of liver disease, your provider may order a blood test to check enzymes. Elevated levels could be a sign of liver disease or other types of disorders. Following a healthy lifestyle and avoiding drugs and alcohol can help enzyme levels return to normal.