What are AST and ALT. How do these liver enzymes indicate liver health. What causes abnormal AST and ALT levels. What are the symptoms of liver dysfunction. How are high AST and ALT levels treated.

The Importance of AST and ALT in Liver Function Assessment

Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are crucial enzymes used to evaluate liver health. These liver function tests provide valuable insights into potential liver damage or disease. Understanding the normal ranges, causes of abnormal levels, and implications of AST and ALT results is essential for proper diagnosis and treatment of liver conditions.

What are AST and ALT?

AST, also known as serum glutamic-oxaloacetic transaminase (SGOT), and ALT are enzymes found primarily in liver cells. When liver cells are damaged or die, these enzymes are released into the bloodstream. Elevated levels of AST and ALT in the blood can indicate liver cell injury or disease.

Normal Ranges for AST and ALT

The normal ranges for AST and ALT can vary slightly depending on the laboratory and testing method. However, generally accepted ranges are:

• AST: 5 to 40 units per liter (U/L)
• ALT: 7 to 56 U/L

It’s important to note that these ranges may differ based on factors such as age, gender, and individual laboratory standards.

Interpreting High AST and ALT Levels

Elevated AST and ALT levels can indicate various liver conditions or damage. The severity of the elevation often correlates with the extent of liver injury.

Mild to Moderate Elevations

Mild to moderate elevations are typically defined as levels less than twice the upper limit of normal. These elevations may be caused by:

• Fatty liver disease
• Chronic hepatitis
• Alcohol consumption
• Certain medications
• Obesity

Marked Elevations

Marked elevations, usually considered to be more than ten times the upper limit of normal, may indicate more severe liver damage. Potential causes include:

• Acute viral hepatitis
• Drug-induced liver injury
• Ischemic hepatitis
• Autoimmune hepatitis
• Acute bile duct obstruction

Causes of Abnormal AST and ALT Levels

Understanding the various factors that can lead to abnormal AST and ALT levels is crucial for accurate diagnosis and treatment.

Acute Viral Hepatitis

Viral hepatitis, particularly hepatitis A, B, and C, can cause significant elevations in AST and ALT levels. These infections lead to inflammation and damage to liver cells, resulting in the release of these enzymes into the bloodstream.

Drug-Induced Liver Injury (DILI)

Certain medications, both prescription and over-the-counter, can cause liver damage and elevate AST and ALT levels. Common culprits include acetaminophen, statins, and some antibiotics.

Alcoholic Liver Disease

Chronic alcohol consumption can lead to alcoholic liver disease, characterized by elevated AST and ALT levels. In alcoholic liver disease, the AST/ALT ratio is often greater than 2, which can help distinguish it from other causes of liver injury.

Nonalcoholic Fatty Liver Disease (NAFLD)

NAFLD, often associated with obesity and metabolic syndrome, can cause mild to moderate elevations in AST and ALT levels. As the condition progresses, these elevations may become more pronounced.

Symptoms Associated with Elevated AST and ALT Levels

While elevated AST and ALT levels themselves do not typically cause symptoms, the underlying liver conditions may present with various signs and symptoms.

Common Symptoms of Liver Dysfunction

• Fatigue
• Jaundice (yellowing of the skin and eyes)
• Abdominal pain or discomfort
• Nausea and loss of appetite
• Dark urine
• Pale stools

Severe Symptoms Requiring Immediate Medical Attention

In cases of acute liver failure or severe liver disease, more serious symptoms may occur:

• Confusion or disorientation (hepatic encephalopathy)
• Severe abdominal pain
• Persistent vomiting
• Easy bruising or bleeding

Diagnostic Approach for Abnormal AST and ALT Levels

When AST and ALT levels are found to be abnormal, a systematic diagnostic approach is essential to determine the underlying cause and assess the severity of liver damage.

Initial Evaluation

The first step in evaluating abnormal AST and ALT levels involves:

1. Detailed medical history, including alcohol consumption, medication use, and risk factors for viral hepatitis
2. Physical examination to assess for signs of liver disease
3. Repeat liver function tests to confirm the abnormality

Further Diagnostic Tests

Depending on the initial findings, additional tests may be necessary:

• Viral hepatitis serologies (Hepatitis A, B, and C)
• Autoimmune markers (ANA, ASMA)
• Imaging studies (ultrasound, CT, or MRI of the liver)
• Liver biopsy (in select cases)

Treatment Strategies for Elevated AST and ALT Levels

Treatment for elevated AST and ALT levels primarily focuses on addressing the underlying cause of liver damage.

Lifestyle Modifications

For many cases of mild to moderate elevations, lifestyle changes can be effective:

• Abstaining from alcohol
• Weight loss and improved diet for NAFLD
• Discontinuation of hepatotoxic medications (under medical supervision)

Medical Interventions

Specific treatments may be necessary depending on the underlying condition:

• Antiviral therapy for viral hepatitis
• Immunosuppressive medications for autoimmune hepatitis
• Targeted therapies for other identified causes

Monitoring and Follow-up of AST and ALT Levels

Regular monitoring of AST and ALT levels is crucial for assessing treatment efficacy and disease progression.

Frequency of Monitoring

The frequency of AST and ALT monitoring depends on the underlying condition and severity of initial elevation:

• Mild elevations: Every 3-6 months
• Moderate to severe elevations: Monthly or more frequently, as determined by a healthcare provider

Long-term Management

Long-term management of patients with a history of elevated AST and ALT levels involves:

• Ongoing lifestyle modifications
• Regular check-ups with a healthcare provider
• Screening for complications of chronic liver disease

Understanding AST and ALT ranges and their implications is crucial for effective liver health management. By recognizing the causes, symptoms, and appropriate diagnostic and treatment approaches for abnormal AST and ALT levels, healthcare providers and patients can work together to maintain optimal liver function and overall health. Regular monitoring and proactive management of these liver enzymes play a vital role in preventing and addressing liver diseases, ultimately contributing to better long-term health outcomes.

Mild to Moderate Aminotransferase Elevation

Abnormal liver test > Hepatocellular pattern > Acute > Mild to moderate ALT/AST elevation

Introduction

Unlike the limited differential diagnosis for marked elevations of AST and ALT, the potential etiologies of mild to moderate acute aminotransferase elevations is extensive, and include all causes of marked AST/ALT elevation. If the elevation is mild (less than twice the upper limit of normal), liver tests should be repeated prior to embarking on an extensive workup. If the abnormality persists, the initial evaluation is the same as the workup for marked ALT/AST elevations and the following etiologies may be considered:.

• Acute viral hepatitis
• Drug-induced liver injury (DILI)
• Toxin-induced liver injury
• Ischemic hepatitis
• Autoimmune hepatitis
• Acute Budd-Chiari syndrome
• Acute bile duct obstruction

In addition, the following etiologies may be considered if suggested by history and physical examination:

• Acute alcoholic hepatitis
• Wilson disease

Though more commonly associated with marked elevation of ALT/AST, fulminant hepatic failure may occur with any type of acute hepatocellular injury. In addition to determining the possible etiology, it is essential to determine the presence of hepatic dysfunction, as evidenced by encephalopathy (confusion, asterixis) and coagulopathy (prolonged INR).

History

Initial questions aimed at determining the possible etiology of acute hepatocellular injury are:

To investigate acute viral hepatitis:

History of blood transfusion, intravenous drug use, unsafe sexual practices, and ingestion of raw shellfish within the last six months.

To investigate drug-induced liver injury:

Detailed medication history including over-the-counter medication, herbal remedies and health food supplements, particularly regarding recently prescribed medications

To investigate toxin-induced liver injury:

Detailed diet/environmental/occupational history, as well as illicit drug use (particularly cocaine)

To investigate ischemic liver injury

Recent (within a day or so) symptoms or conditions associated with a low perfusion state such as pre-syncopal or syncopal episodes, hypotension, arrhythmias, low cardiac ejection fraction.

To investigate autoimmune hepatitis

Family or personal history of autoimmune disorders such as thyroiditis, hyper or hypothyroidism, lupus, rheumatoid arthritis, vitiligo

To investigate acute Budd-Chiari syndrome:

Presence of abdominal distension (ascites) with or without peripheral edema and right upper quadrant pain.

To investigate acute bile duct obstruction:

Compatible clinical picture with epigastric or right upper quadrant pain, a history of biliary surgery and/or gallstones.

Physical examination

In general, there are no specific findings for acute hepatocellular injury. Jaundice may be present. Viral causes may be accompanied by common findings associated with viral syndrome (fever, rash, lymphadenopathy).

It is however essential to check for signs of hepatic encephalopathy (confusion, asterixis). Patients with confusion and/or asterixis should be urgently referred to a liver specialist or a transplant center.

Laboratory Investigation

Initial investigation should be directed at evaluating the presence of hepatic dysfunction and investigating the etiology of the acute hepatitis.

Liver biopsy is generally not indicated in acute hepatocellular injury as it will show hepatic necrosis but will not be specific for its etiology.

To evaluate hepatic function:

• Prothrombin time (PT) and INR
  Patients with abnormal prothrombin time or INR should be urgently referred to a liver specialist or a transplant center.

To investigate acute viral hepatitis:

• Hepatitis A antibody of the IgM type (IgM anti-HAV)
• Hepatitis B core antibody of the IgM type (IgM anti-HBc)
• Hepatitis B surface antigen (HBsAg)
• Hepatitis C antibody (anti-HCV)
• Consider HBV-DNA titer* and HCV-RNA titer*
• Serologies and/or PCR for CMV, EBV and HSV (if the tests above are non-revealing)

*In the very early course of acute hepatitis B or C or in the immunocompromised patient, viral serologies may be negative. PCR testing should be obtained if suspicion for recent infection is high (for example, history of IV drug use or unsafe sexual contact within the last six months) or in the immunocompromised patient.

To investigate autoimmune hepatitis:

• Antinuclear antibodies (ANA)
• Anti-smooth muscle antibody (ASMA)
• Serum protein electrophoresis (SPEP)

To investigate toxic damage:

• Toxicology screen

To investigate acute alcoholic hepatitis:

• AST/ALT ratio usually greater than 2

To investigate Wilson’s disease (WD):

• Ceruloplasmin levels
• Alkaline phosphatase (frequently low in WD)
• Alkaline phosphatase/bilirubin ratio lower than 2

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AST

Also Known As

Serum glutamic-oxaloacetic transaminase (SGOT)

At a Glance

Why Get Tested?

To detect liver damage

When To Get Tested?

If your doctor thinks that you have symptoms of a liver disorder

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual’s health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

AST is an enzyme found mostly in the heart and liver and to a lesser extent in skeletal muscle. When heart, liver or muscle cells are injured, they release AST into the bloodstream.

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Common Questions

• How is it used?

  Testing for AST is usually used to detect liver damage.

  AST results can be examined alongside concentrations of other liver enzymes, such as alkaline phosphatase (ALP), and alanine transaminase (ALT), to determine which form of liver disease is present.

  Even though AST is found in heart and other muscles, another enzyme, creatine kinase (CK), is present in much higher amounts and is usually used to detect heart or muscle injury.

• When is it requested?

  An AST blood test is usually requested alongside several other tests to help evaluate a patient who has symptoms of a liver disorder. Some of these symptoms include jaundice (yellowing of the eyes and skin), dark urine, nausea, vomiting, abdominal swelling, unusual weight gain, and abdominal pain. AST can also be requested, either by itself or with other tests, for:

  • persons who might have been exposed to hepatitis viruses,
  • those who drink too much alcohol,
  • persons who have a history of liver disease in their family, or
  • persons taking drugs that can occasionally damage the liver.

  Individuals who have mild symptoms, such as tiredness, may have AST measured  to make sure they do not have long-term (chronic) liver disease. AST is often measured to monitor treatment of persons with liver disease, and may be requested either in isolation or alongside other tests.

• What does the test result mean?

  Very high concentrations of AST (more than 10 times the upper limit of normal (ULN)) are usually due to a rapidly developing liver disease called acute hepatitis, which is often caused by a virus or by toxins/drugs such as paracetamol overdose. In acute viral hepatitis, AST concentrations usually stay elevated for about 1–2 months, but can take as long as 3–6 months to return to normal.

  Moderately high levels, often less than 4 times the upper limit of normal (ULN) are seen in the slowly developing variety of liver disease, chronic hepatitis, as well as alcohol abuse, cholestasis and heart, kidney or skeletal muscle damage The AST level can also be increased following the breakdown of red blood cells (haemolysis). In chronic hepatitis, AST often varies between normal and slightly increased, so doctors might request the test regularly to determine the pattern of change.

  In some diseases of the liver, especially when the bile ducts are partially blocked, fatty change in the liver or with cirrhosis and certain cancers of the liver, AST concentrations may be slightly high or close to normal.

  In chronic viral hepatitis, chronic alcoholism or non-alcoholic fatty liver disease a high AST/ALT ratio may be used to predict long-term complications such as cirrhosis.

• Is there anything else I should know?

  An injection of medicine into muscle tissue, or even strenuous exercise, may increase AST concentrations within the bloodstream. In rare instances, some drugs can damage the liver or muscle, increasing AST concentrations. This is true of both prescription drugs and some ‘natural’ or herbal health products. If your doctor finds that you have high levels of AST, tell him or her about all the drugs and health products you are taking.

• What other tests are used to evaluate liver disorders?

  Other commonly used liver tests include more enzymes found in liver cells, such as alanine transferase (ALT) and alkaline phosphatase (ALP), as well as bilirubin (a yellow pigment removed from the body by the liver).