Meaning of Low, Normal, High Levels

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Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are two of the liver enzymes health care providers look at when trying to find out if you have a problem with your liver. Liver enzymes are substances produced by the liver that can be measured with a blood test. A high ALT level or a high AST level can be a sign of a liver problem.

When compared, ALT and AST levels can help identify toxins in the liver, liver disease, or liver damage.

This article will discuss the liver enzymes ALT and AST. It will talk about what they do inside your body and what happens when you have elevated ALT or AST levels.

Verywell / Elise Degarmo

When to test?

ALT and AST levels are measured as part of a comprehensive panel called a liver function test (LFT). An LFT can be ordered:

  • If you have symptoms of liver disease, including jaundice, dark urine, nausea, vomiting, and fatigue
  • To monitor the progression of liver disease
  • To determine when to start certain drug treatment
  • To check your response to liver treatments

LFT can also determine whether a drug (prescription or over-the-counter) or an herbal remedy is causing liver damage.

If the lab test is processed on-site, results can be returned within hours. Otherwise, your doctor will usually get the results within one to three days.

The role of AST and ALT

Aminotransferases These are chemicals that the liver uses to make glycogen. Glycogen is the storage form of glucose, the sugar the body uses for energy.

Any glucose that is not used immediately is converted to glycogen. It is then stored in cells for future use. Much of it will be stored in the liver. The remaining amount will be stored in:

Aspartate aminotransferase (AST) found in many types of tissues, including liver, brain, pancreas, heart, kidney, lung, and skeletal muscle. If any of these tissues are damaged, AST is released into the bloodstream. While a high AST level means there may be tissue damage, it doesn’t always involve the liver.

Opposite, alanine aminotransferase (ALT) Found mainly in the liver. High ALT levels are always worrisome, but they don’t necessarily indicate something serious. If your ALT level is high, it may indicate mild or severe liver damage.

Occasional ALT elevations can occur when you have a short-term infection or illness. The continuous increase is more and more serious. That’s because this can mean there is an underlying disease and a higher chance of liver damage.

Normal laboratory value

AST and ALT are measured in international units per liter (IU/L). Normal levels vary based on a person’s body mass index (BMI). It also depends on the laboratory reference value or typical results.

In general, a normal AST level for an adult is: 8 to 48 IU/L. A normal ALT level for an adult is 7 to 55 IU/L.

The highest value of the reference range is called the upper limit of normal (ULN). This number is used to determine how elevated your liver enzymes are.

Mild elevation is generally considered to be two to three times the ULN. With some liver diseases, levels can be more than 50 times the ULN. This high level is described as deranged.

AST/ALT . Ratio

While it may seem that a high ALT is all that is needed to diagnose liver disease, its relationship with the AST can provide valuable clues as to what exactly is going on. It will also tell you whether the problem is acute (occurs suddenly and progresses rapidly) or chronic (long-term or persistent).

If the liver has suffered an acute injury, you may see a spike in ALT. Conversely, if liver disease progresses slowly, the damage to the liver over time will affect other organs. When these organs are damaged, the AST will begin to rise.

This happens with diseases like hepatitis C. It causes long-term liver damage that causes symptoms related to:

  • Kidney
  • Brain
  • Look
  • Skin
  • Coupling

These are called extrahepatic symptoms.

The relationship between these enzymes is described using the AST/ALT ratio. This is a calculation that compares the levels of AST and ALT in your blood. Depending on which values ​​are raised and how elevated, doctors can often get a pretty clear indication of which disease is involved.

What does the AST/ALT ratio reveal?

The AST/ALT ratio is important because its pattern can tell a lot about the condition involved. The following are general guidelines used to diagnose liver disease:

  • An AST/ALT ratio of less than one (where ALT is significantly higher than AST) means you may have nonalcoholic fatty liver disease.
  • An AST/ALT ratio of one (where ALT is equal to AST) may be indicative of acute viral hepatitis or drug-induced hepatotoxicity.
  • An AST/ALT ratio higher than one (where AST is higher than ALT) means you may have cirrhosis.
  • An AST/ALT ratio higher than 2:1 (where AST is more than twice the ALT) is a sign of alcoholic liver disease.

However, a disease cannot be diagnosed by elevation modeling alone. How much of an increase also needs to be measured. This is described in multiples of the ULN. Only when levels are above a certain threshold can this ratio be considered diagnostic.


The AST/ALT ratio is a comparison of the levels of two enzymes. This measurement can indicate liver disease, but only if enzyme levels are several times higher than normal.


Liver enzymes ALT and AST are produced by the liver. Doctors can check these levels with a blood test. If you have elevated liver enzymes, it could be a sign that you have liver disease.

AST is found in the liver, brain, pancreas, heart, kidneys, lungs, and skeletal muscle. ALT is found mainly in the liver.

If your AST level is too high, it could be a sign of injury affecting tissues other than the liver. A high ALT level may mean you are suffering from liver injury. It could also be a sign that you have an infection or a short-term illness.

The ratio of the two enzymes can help diagnose specific liver diseases.

frequently asked Questions

  • What does a high AST level mean?

    A high AST (aspartate aminotransferase) level may indicate a problem with your liver. However, it usually doesn’t mean you have a medical condition that needs to be treated. It could be a side effect of the medication. Very high AST levels can indicate hepatitis, cirrhosis, mononucleosis, heart problems, or pancreatitis.

  • What AST level is considered high?

    The upper limit of normal for AST is 48 IU/L. Levels two to three times the upper limit of normal are considered mildly elevated. In liver disease, AST levels can be 50 times the upper limit of normal. The medical term for this is degrees of deviance.

  • What does a high ALT level mean?

    High alanine transaminase (ALT) levels can indicate a liver problem but does not necessarily mean you have a medical condition. Very high ALT levels may suggest liver damage from hepatitis, infection, liver cancer, or liver disease. High ALT levels can also be a side effect of some medications.

  • What ALT levels are considered high?

    The upper limit of normal for ALT is 55 IU/L. When the ALT level doubles to three times the upper limit of normal, it is considered mildly elevated. The severely elevated ALT levels found in liver disease are often 50 times the upper limit of normal.

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