AST, or aspartate aminotransferase, is an enzyme found in the liver, heart, kidneys, muscles, pancreas and other organs. It plays an important role in metabolism. When the level of AST in the blood is elevated, it usually indicates some sort of damage or injury to tissues containing AST. Some common causes of elevated AST include:
Liver Damage
The liver contains high concentrations of AST. When the liver is damaged or inflamed, AST levels in the blood rise. Some common causes of high AST related to liver problems include:
– Viral hepatitis – Hepatitis A, B and C infections can cause inflammation that raises AST.
– Alcoholic liver disease – Heavy alcohol use over many years can lead to fatty liver, alcoholic hepatitis and cirrhosis. All of these conditions cause AST elevations.
– Nonalcoholic fatty liver disease – Buildup of fat in the liver, often associated with obesity, insulin resistance and diabetes.
– Medications and supplements – Certain over-the-counter pain relievers like acetaminophen and some cholesterol or blood pressure medications can be toxic to the liver in high doses.
– Autoimmune disorders – Diseases like autoimmune hepatitis where the immune system attacks liver cells.
– Congestive heart failure – Impaired heart function can cause fluid to back up in the liver, raising AST.
Heart Damage
Because AST is found in heart muscle cells, injury to the heart can lead to high levels. Conditions that may elevate AST due to heart damage include:
– Heart attack – When blood flow to part of the heart muscle is blocked, cardiac cells die and release AST into the blood.
– Myocarditis – Inflammation or infection of the heart muscle often causes cell damage and leaking of AST.
– Congestive heart failure – Chronic heart failure leads to damage and death of cardiac cells.
– Cardiomyopathy – Disease of the heart muscle like hypertrophic cardiomyopathy where the heart walls abnormally thicken.
Muscle Damage
Skeletal muscle contains AST, so damaged muscle releases AST into the circulation. Causes include:
– Trauma – Any trauma like a car accident or significant fall that damages muscle can raise AST. Crush injuries are a common cause.
– Burns – Severe burns often involve damage to muscle tissue and elevated AST.
– Intense exercise – Very strenuous exercise can cause minor muscle fiber and cell damage leading to mild AST increase.
– Muscular dystrophy – Degenerative diseases like muscular dystrophy cause progressive muscle wasting and AST leaks out.
– Seizures – Violent muscle contractions during seizures can result in rhabdomyolysis and AST elevations.
Pancreatitis
The pancreas contains AST so any pancreatic inflammation or damage raises levels. Gallstones and heavy alcohol use are common causes of pancreatitis.
What Level of AST is Considered High?
The normal range for AST levels can vary slightly between labs but is generally:
– Adult males: 10-40 units/liter
– Adult females: 10-32 units/liter
Mildly Elevated AST
AST levels that are above the normal limit but less than twice the upper end of normal are considered mildly elevated. This may be seen in:
– Mild liver cell damage from fatty liver disease or alcohol
– Muscle trauma from exercise or injury
– Early viral hepatitis infection
– Resolving heart damage from myocardial infarction
Moderately Elevated AST
When AST levels are more than twice normal but less than 10 times higher than the upper limit, this is considered moderately elevated. This degree of AST increase may be present with:
– Alcoholic hepatitis
– Acetaminophen toxicity
– Acute viral hepatitis
– Acute myocarditis
– Muscle damage from trauma/burns
– Pancreatitis
Severely Elevated AST
AST levels more than 10 times elevated over the upper normal limit indicate significant tissue damage and inflammation. Severe AST increases are seen in conditions like:
– Viral or autoimmune hepatitis
– Acute liver failure
– Shock liver from low blood pressure
– Heart attack with extensive myocardial damage
– Rhabdomyolysis with severe muscle breakdown
What Other Liver Tests are Used with AST?
AST is almost never used alone to evaluate liver disease. Physicians will usually order a panel of liver function blood tests including:
ALT – Alanine Aminotransferase
ALT is another enzyme found predominantly in the liver. It is often checked together with AST to help determine the source of liver cell damage. In alcoholic liver disease, AST is usually higher than ALT. But in viral hepatitis, ALT is typically higher than AST.
Alkaline Phosphatase
Alkaline phosphatase (ALP) is an enzyme present in liver bile ducts. Elevated ALP along with AST points more towards a bile duct source of liver injury like primary biliary cirrhosis or drug-induced cholestasis.
Bilirubin
Bilirubin is formed from the breakdown of old red blood cells in the liver. Increased bilirubin with elevated AST indicates impairment in liver excretory function and more severe liver disease.
Albumin
Albumin and other proteins are produced in the liver. Low blood albumin levels paired with high AST show compromised liver synthetic function.
AST to ALT Ratio
Looking at the ratio between AST and ALT levels can provide useful diagnostic information about the source of liver damage.
| AST to ALT ratio | Associated condition |
|---|---|
| AST > 2 x ALT | Alcoholic liver disease |
| AST < ALT | Viral hepatitis, fatty liver disease |
| AST = ALT | Drug toxicity, shock liver |
For example, a AST to ALT ratio of 1.5 would point more towards alcohol as the cause of liver injury. While a ratio of 0.8 would indicate hepatitis or fatty liver disease as more likely.
What Other Conditions Lead to High AST?
Besides damage to the liver, heart and muscles, some other causes of elevated AST include:
Cancer
Cancers that have spread to the liver or invaded muscle may raise AST levels. Lung, colon, breast and stomach cancers are most likely to metastasize to these organs.
Hypothyroidism
Thyroid hormones help regulate AST levels in tissues. Low thyroid function can slow normal clearance of AST and cause levels to rise.
Medications
As mentioned previously, certain prescription drugs like statins, methotrexate, anti-seizure medications and antibiotics can cause liver toxicity and high AST.
Macro-AST
In rare cases, the AST molecule becomes bound to immunoglobulins in the blood. This creates a macro-AST complex that is too large to be filtered by the kidneys. Levels can become chronically elevated even without tissue injury.
How to Lower High AST Levels
Treating the underlying cause of AST elevation is key to reducing levels. However, there are some general measures that may help lower AST:
Avoid alcohol
Alcohol is metabolized by the liver and directly toxic to liver cells. Eliminating alcohol intake allows liver inflammation to resolve.
Manage heart health
Controlling conditions like high cholesterol, diabetes and high blood pressure reduces the risk of heart damage that could raise AST. Medications can also treat heart failure.
Limit medication doses
Avoid exceeding maximum recommended doses of hepatotoxic drugs like acetaminophen, certain statins or cholesterol medications.
Treat infections
For AST elevations due to hepatitis, medications can treat the viral infection and limit further liver cell damage.
Avoid strenuous exercise
Let damaged muscles fully recover before intense physical exertion to prevent recurrent rhabdomyolysis episodes.
Control diabetes
Managing blood sugar and hemoglobin A1C levels can help prevent damage to organs like the liver, heart and muscles.
Immunosuppressants
For autoimmune hepatitis, steroids and other drugs can calm the overactive immune response attacking the liver.
When to See a Doctor
You should see a doctor if you have any symptoms of liver disease like abdominal pain, nausea, fatigue or yellow skin along with elevated AST. It is also important to get prompt evaluation for:
– AST over 500 units/L which indicates acute liver injury
– AST over 250 units/L with elevated bilirubin which signals impaired liver function
– Persistent moderate AST elevation that does not resolve spontaneously
– AST elevations along with reduced albumin or blood cell counts
– AST over 1000 units/L which suggests extensive tissue damage
Your doctor will take into account your full clinical picture including risk factors, symptoms, physical exam findings and results of other liver tests when assessing the significance of an elevated AST. They can order imaging tests like an abdominal ultrasound or CT scan to look for structural abnormalities in the liver. Viral hepatitis blood panels may be ordered to identify an infectious cause.
In most cases, following up with repeat AST testing is needed to monitor a falling trend back to normal levels. However, persistently high AST over months requires more extensive investigation to rule out chronic liver diseases, heart conditions or other serious disorders.
Conclusion
An elevated AST level indicates damage or injury to tissues that contain AST enzymes, especially the liver. Mild increases can occur from minor muscle trauma, but more significant elevations point to organ damage from conditions like viral hepatitis, heart attack, liver cirrhosis or severe rhabdomyolysis. However, AST is just one piece of the puzzle, and your doctor will interpret your AST result in the context of your full clinical presentation and results of other liver function tests. Treating underlying causes like alcoholism, diabetes or infections can help resolve AST abnormalities. But severely high or persistent AST warrants further evaluation to assess for serious medical conditions and prevent complications.