Alanine-aminotransferase (ALT), formerly called serum glutamic pyruvic transaminase, is an enzyme produced by the liver and found in blood. Its primary function is to serve as a catalyst for chemical reactions. A healthy human body will naturally display low levels of ALT; however, when the liver is damaged or diseased it will release ALT into the bloodstream causing ALT levels to rise. As such, an ALT test is typically done to identify liver diseases, especially cirrhosis and hepatitis. ALT tests can also be used to keep track of medications that can damage the liver. If a person has jaundice (yellowing of the skin or eyes) an ALT test can determine whether a blood disorder or liver disease is the cause. However, ALT is a liver-specific enzyme and elevated levels typically indicate a problem with liver cell integrity. Further, ALT tests may be done in tandem with an alkaline phosphatase test to distinguish liver damage from a bile duct problem.
Normal Ranges in U/L:
Male: 5-63 U/L
Female: 5-54 U/L
- Decreased ALT levels are associated with a B6 deficiency.
- A low level of ALT in the blood is typical and healthy for an adult.
Slightly high ALT levels may be caused by:
- Alcohol abuse
- Cirrhosis (long-term damage and scarring of the liver)
- Drugs such as statins, aspirin, and some sleep aids
Moderately high ALT levels may be because of:
- Chronic (ongoing) liver disease
- Alcohol abuse
- Blockage of the bile ducts
- Heart attack or heart failure (when your heart can’t pump enough blood to your body)
- Kidney damage
- Muscle injury
- Damage to red blood cells
- Heat stroke
- Too much vitamin A
Very high ALT levels can be caused by:
- Acute viral hepatitis
- An overdose of drugs such as acetaminophen (Tylenol)
- Liver cancer
An ALT test whose value is twenty or fifty fold the normal range indicates damage to the liver. Liver diseases like hepatitis and cirrhosis may be the cause of the damage.
Symptoms of liver disease include:
- Jaundice, or yellow skin
- Unexpected weight loss
- Swelling around the eyes, stomach, or legs
There are also many medications that have the potential to damage the liver, including: antibiotics, chemotherapy, aspirin, narcotics, and barbiturates. It is worth noting that levels of ALT fluctuate throughout the day and can also increase significantly in response to strenuous physical exercise.
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