What is an alanine aminotransferase (ALT) blood test?
Besides helping the liver break down proteins, ALT helps the liver perform its basic functions. Some of these include:
- filtering toxins from the blood
- storing nutrients and iron
- producing bile, which aids digestion
Most ALT that the liver produces stays within the organ. However, when the liver is damaged or inflamed, it may release ALT into the bloodstream.
When this happens, the level of ALT in the blood rises. Therefore, doctors use an ALT blood test to screen for liver disease or damage. Learn more about the test in this article.
An ALT test can help a doctor diagnose various liver conditions.
A doctor orders an ALT test to look for problems with liver function. Many people have this test as part of a comprehensive metabolic panel.
The comprehensive metabolic panel is a routine blood test that checks a person's glucose level, kidney function, and liver function. It is often part of a routine checkup that gives a doctor insight into an individual's overall health.
Other times, a doctor orders the ALT blood test as part of a series of blood tests called liver panels if they suspect that a person's liver is damaged or diseased.
Doctors may order liver panels if a person has symptoms of liver disease or damage. Symptoms of liver problems include:
- yellowing of the eyes and skin (jaundice)
- pain in the upper right quadrant of the abdomen
- referred pain in the right shoulder
- easy bleeding or bruising
- intense itching
- pale stools
- swelling in legs or abdomen
These symptoms can indicate liver disease, injury, or another problem that may be affecting the liver.
Medical problems that can cause elevated ALT levels include:
- nonalcoholic fatty liver disease
- celiac disease
- thyroid disorders
- preeclampsia in pregnant or immediately postpartum women
- certain infections, including mononucleosis and sepsis
- Wilson's disease
- liver cancer
Certain medications can also cause ALT levels in the blood to be high.
Often, these levels are elevated before symptoms of liver damage occur, making the test useful for people at risk of liver damage.
When a doctor can detect liver damage early, they may be better able to treat it and prevent further injury.
People at risk of liver damage or disease include:
- people with a family history of liver disease
- people who have diabetes
- people who are overweight
- people who consume a lot of alcoholic beverages
- people taking certain medications
Doctors routinely order liver panels to monitor diagnosed liver disease or injury. The results of these tests can show how well the treatment plan is working.
Understanding the results
A doctor can explain the results of an ALT test in detail.
A person with a healthy liver will have an ALT level in the normal range. The normal range can vary from laboratory to laboratory.
According to the Mayo Clinic, the normal range for adult males is 7–55 units per liter. Females may have a lower upper limit normal than males.
Age can also affect results. A person should speak with their doctor about what their results mean.
If a person has results above the normal range, this may indicate liver damage.
Causes of elevated ALT levels include:
- the destruction of liver cells
- a lack of blood flow to the liver
- cirrhosis, or severe scarring of the liver
- hemochromatosis, or iron buildup
- mononucleosis, an infection usually caused by the Epstein-Barr virus
- a tumor in the liver
A person should discuss their results with their doctor, who can say if the numbers returned are within a normal range.
If a person's results are too low or high, a doctor can help determine the appropriate course of treatment.
People with higher ALT levels often need additional tests to discover the underlying cause of the liver damage and treat it.
An ALT blood test helps determine if a person has liver damage. Uncovering the cause of the problem often requires further testing.
The normal range for results tends to vary among facilities, and a doctor can discuss what the results mean on an individual basis.
Once they know the underlying cause of the liver damage, based on symptoms and test results, the doctor will discuss appropriate treatment options.