When cells in the body are damaged, they can release certain enzymes into the bloodstream. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are two such enzymes, commonly measured in routine blood tests. Primarily found within liver cells, where they help convert food into energy, AST and ALT levels rise when liver cells are injured or inflamed and leak out. Elevated levels often signal a need for further investigation to determine the underlying cause of cellular damage, particularly within the liver.
Understanding AST and ALT
AST and ALT are specialized proteins that facilitate chemical reactions within cells, involved in amino acid metabolism. Alanine aminotransferase (ALT) is predominantly concentrated in the liver, making it a more specific indicator of liver health. Aspartate aminotransferase (AST), while abundant in the liver, is also present in other tissues like the heart, skeletal muscles, and kidneys. Both enzymes are typically found at low levels in the bloodstream. When cells containing these enzymes are damaged, they escape into circulation, leading to detectable increases in blood levels. Their measurement is a common component of liver function tests.
Common Causes of Elevated Liver Enzymes
One of the most frequent reasons for elevated AST and ALT is metabolic dysfunction-associated steatotic liver disease (MASLD). This condition involves excess fat accumulation in the liver, often associated with obesity, type 2 diabetes, and high cholesterol. MASLD can progress to metabolic dysfunction-associated steatohepatitis (MASH), a more severe form with liver inflammation and damage.
Excessive alcohol consumption is another common cause of liver enzyme elevation, leading to alcoholic liver disease. Alcohol directly damages liver cells, causing the release of AST and ALT into the bloodstream. This chronic damage can range from fatty liver to more severe conditions like alcoholic hepatitis or cirrhosis.
Viral infections, such as hepatitis A, B, and C, are also significant contributors to elevated liver enzymes. These viruses cause inflammation and damage to liver cells, resulting in the release of transaminases. Both acute and chronic forms of viral hepatitis can lead to increased AST and ALT levels.
Certain medications and toxins can induce liver injury. Common culprits include high doses of acetaminophen, some antibiotics, and statins. The liver processes many substances, making it susceptible to damage from various drugs, herbal supplements, or environmental toxins.
Less common, but still significant, liver-related causes include autoimmune hepatitis, where the body’s immune system attacks liver cells, and hemochromatosis, a genetic disorder leading to excessive iron accumulation in the liver. These conditions can also cause persistent inflammation and damage, resulting in elevated enzyme levels.
Other Potential Causes of Elevated Liver Enzymes
While often associated with the liver, elevated AST and ALT can also stem from conditions affecting other parts of the body. Since AST is present in skeletal muscle, significant muscle damage can lead to its elevation. Intense physical exertion, muscle injuries, or severe conditions like rhabdomyolysis can cause muscle cells to release AST into the bloodstream.
Heart conditions, particularly a heart attack, can also result in elevated AST levels. The heart muscle contains AST, and damage to this tissue during a heart attack causes the enzyme to be released into circulation. This elevation is generally more pronounced for AST than ALT.
Thyroid disorders, such as hyperthyroidism, sometimes contribute to mild elevations of liver enzymes. This is believed to involve metabolic changes affecting liver function.
Celiac disease, an autoimmune disorder triggered by gluten consumption, has also been linked to mild, unexplained elevations in AST and ALT in some individuals. Rarer genetic conditions, such as Wilson’s disease (copper accumulation) or alpha-1 antitrypsin deficiency (affecting protein production), can also lead to liver damage and elevated enzymes.
What Elevated Levels Mean and Next Steps
Elevated AST and ALT levels serve as important indicators of potential cellular injury, but they do not provide a definitive diagnosis. These results suggest further medical evaluation is necessary to pinpoint the underlying cause. Consulting a healthcare professional is crucial for proper interpretation of these enzyme levels within the context of an individual’s overall health and symptoms.
A doctor will typically order additional diagnostic tests to investigate the source of the elevation. These may include other blood tests, such as bilirubin, alkaline phosphatase, and gamma-glutamyl transferase (GGT), which provide more comprehensive insights into liver function.
Imaging studies like ultrasound, CT scans, or MRI of the abdomen can visualize the liver and surrounding organs for structural abnormalities. In some instances, a liver biopsy, involving the removal of a small tissue sample for microscopic examination, may be performed to determine the extent and nature of liver damage.
The ratio between AST and ALT can sometimes offer clues about the type of liver damage. For example, an AST:ALT ratio greater than 2 often suggests alcoholic liver disease, while a ratio less than 1 is more common in acute viral hepatitis or fatty liver disease. Identifying and addressing the specific cause of elevated enzyme levels is essential for effective management and to help prevent further organ damage.