Receiving a blood test result with elevated liver enzymes can be worrying. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are enzymes primarily found in the liver that help with metabolic processes like breaking down amino acids. When liver cells are damaged or inflamed, they release these enzymes into the bloodstream, leading to higher levels on a blood test. However, elevated AST and ALT are non-specific indicators of liver stress with a wide range of possible causes.
The Link Between Liver Enzymes and Cancer
Cancer can elevate AST and ALT levels through direct damage to the liver. This occurs with cancer that originates in the liver (primary liver cancer) and cancer that spreads to it. The most common form of primary liver cancer, hepatocellular carcinoma (HCC), is associated with pre-existing liver conditions like cirrhosis or chronic hepatitis. As the tumor grows, it destroys healthy liver cells, causing them to release AST and ALT into the bloodstream.
The liver’s extensive blood supply makes it a common site for metastasis, where cancer from another organ spreads. Cancers originating in the colon, lung, breast, pancreas, or stomach can travel through the bloodstream and establish secondary tumors in the liver. Up to 70% of individuals with colorectal cancer may eventually develop liver metastases. These metastatic tumors disrupt the liver’s structure and function, leading to inflammation and damage of surrounding healthy liver tissue.
Common Non-Cancerous Causes of Elevated Liver Enzymes
While cancer is a concern, it is not the most frequent reason for elevated liver enzymes, which are often caused by common, non-cancerous conditions. Among the most prevalent is nonalcoholic fatty liver disease (NAFLD), characterized by the accumulation of excess fat in the liver and associated with obesity and metabolic syndrome. Alcoholic liver disease, from excessive alcohol consumption, is another major contributor.
Viral infections that target the liver, such as Hepatitis A, B, and C, are a frequent source of the inflammation that elevates AST and ALT. Certain medications can also be responsible for liver stress. These include high doses of over-the-counter pain relievers like acetaminophen, some prescription drugs like statins, and some herbal supplements.
Other medical conditions can also cause elevated enzymes. Autoimmune hepatitis, a disorder where the body’s immune system attacks the liver, causes chronic inflammation and elevated enzymes. Celiac disease, an autoimmune reaction to gluten, has also been associated with mild liver enzyme abnormalities. Since AST is also found in muscle tissue, severe muscle injury from intense exercise or trauma can lead to an isolated increase in AST levels.
The Diagnostic Process
Elevated AST and ALT levels are a signal to investigate further, not a final diagnosis. The process begins with a thorough review of your medical history and lifestyle to identify the root cause. Your doctor will ask about your alcohol consumption, any prescription and over-the-counter medications you are taking, and any herbal supplements you use.
Following the initial consultation, further blood work is often the next step. A comprehensive liver panel can provide more detailed information by measuring other substances like alkaline phosphatase (ALP), bilirubin, and albumin to help determine the pattern of liver injury. Specific blood tests to screen for viral hepatitis B and C are also standard procedure.
If the cause of the elevated enzymes is still unclear, imaging studies are ordered to visualize the liver. An abdominal ultrasound is often the first imaging test used, as it can detect fat accumulation, signs of cirrhosis, or blockages in the bile ducts. For a more detailed look, a CT scan or an MRI may be recommended to get a clearer picture of the liver’s structure and to identify any tumors or other abnormalities.
In cases where blood tests and imaging are inconclusive or suggest a more serious condition, a liver biopsy may be considered. During a biopsy, a small sample of liver tissue is removed with a needle and examined under a microscope. This procedure can provide definitive answers about the nature and extent of liver damage, helping to diagnose conditions like advanced fibrosis, autoimmune hepatitis, or cancer.