Alanine Aminotransferase (ALT): A Comprehensive Health Guide

The liver's role in over 500 physiological functions in the human body makes this organ indispensable, yet its silent nature often conceals early signs of distress until advanced disease is present. Experts report that 25% of people have compromised liver function and may not know it. In an era where proactive healthcare is increasingly emphasized, monitoring liver enzymes has emerged as a crucial strategy for early detection and prevention of liver-related diseases.

Alanine aminotransferase (ALT) is a liver enzyme that can be measured in the blood to assess liver health. Elevated ALT levels can be one of the first signs of liver injury and inflammation, often preceding the onset of overt liver disease. Incorporating regular ALT measurements into routine health screenings may help identify subtle changes in liver function, facilitating timely interventions that may halt or reverse the progression of liver pathology. 

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What Is Alanine Aminotransferase (ALT)?

ALT is an enzyme primarily found in the liver. High levels of ALT in the blood may indicate liver inflammation, damage, or disease. Sometimes, ALT is called serum glutamic pyruvic transaminase (SGPT).

The Role of ALT in the Body

An enzyme is a type of protein that helps speed up chemical reactions. Specifically, ALT helps convert alanine, an amino acid (a protein building block), into pyruvate, a molecule used for energy production. 

Where Is ALT Found?

ALT is primarily concentrated inside liver cells (hepatocytes). It is also found in lower concentrations inside cells of the kidneys, skeletal muscles, brain, pancreas, spleen, and lungs. 

It is normal to measure small amounts of ALT in the blood of a healthy individual. However, damage to or inflammation in the liver can cause ALT to leak out of hepatocytes into the bloodstream, resulting in elevated levels on a blood test. 

There are other liver enzymes, including: 

• Aspartate transaminase (AST)
• Alkaline phosphatase (ALP)
• Gamma-glutamyl transferase (GGT)

Unlike ALT, these enzymes are also found in higher amounts in other tissues, such as the heart, skeletal muscles, pancreas, and bones. Consequently, ALT is generally considered to be a more direct marker of liver health. 

How ALT Levels Are Measured

A doctor may order an ALT blood test to assess liver health and function. 

Many times, they will order a comprehensive metabolic panel (CMP) as part of a general health screening. In addition to ALT and AST liver enzymes, this panel measures blood sugar, electrolytes, and kidney function as part of a broad metabolic health assessment. 

Additionally, ALT may be ordered as part of a liver panel if a patient has symptoms indicating an underlying liver condition, has preexisting liver disease, or is taking medications that can negatively affect liver health.

Symptoms of liver problems can include: 

• Upper abdominal pain
• Nausea and vomiting
• Loss of appetite
• Yellowing of the skin and eyes (jaundice)
• Easy bleeding or bruising
• Itching
• Pale stools
• Dark urine
• Swelling in the hands, feet, or abdomen 
• Weight loss
• Fatigue

If you experience any of these symptoms, please consult a healthcare professional for evaluation.

The ALT Blood Test

The ALT blood test is a straightforward procedure that measures the amount of alanine aminotransferase in your blood. A healthcare provider will draw a blood sample from a vein in your arm using a small needle. This procedure is quick and relatively painless. You may feel a slight pinch during needle insertion or removal, and any mild pain or bruising should subside within a few days after the blood draw.

Little preparation is required for this test:

• If your ALT test is part of a CMP, your doctor may ask you to fast for 8-12 hours before the blood draw. Fasting means not eating or drinking anything besides water.
• Sometimes, your doctor may ask you to stop taking a medication or supplement before the test. Never stop a medication unless your doctor tells you. 
• Avoid intense exercise before the test, which can affect ALT levels. 

Always follow your doctor's specific instructions to ensure accurate test results.

Interpreting ALT Levels

The normal range for ALT is 4 to 36 units per liter (U/L). However, this range can vary between different laboratories and institutions. For instance, the Cleveland Clinic cites normal ALT levels as 7 to 56 U/L.

There is ongoing discussion about modifying ALT's reference range. Several studies and guidelines have suggested that the upper limit of normal (ULN) for ALT should be lowered to better identify individuals at risk for metabolic dysfunction-associated steatotic liver disease (MASLD) (previously called non-alcoholic fatty liver disease [NAFLD]). 

For instance, the American College of Gastroenterology (ACG) has proposed a true ULN of 29 to 33 U/L for males and 19 to 25 U/L for females. This proposal is based on evidence suggesting that even ALT levels within the currently accepted normal range may be associated with increased liver-related mortality and significant liver disease. Studies indicate that a lower ALT threshold could improve the detection of MASLD and related conditions. 

Causes of High or Low ALT Levels

When interpreting ALT levels, it is important to remember that this test is one component of a comprehensive medical evaluation. It should always be interpreted by a qualified healthcare professional in the context of a patient's medical history and other laboratory findings. 

An abnormal ALT test alone cannot diagnose a liver condition; further testing is warranted to determine the underlying cause. Possible causes of abnormal ALT results are highlighted below: 

High ALT Levels

Increased ALT levels may be a result of: 

• Hepatitis: liver inflammation caused by various causes, such as viral infections, heavy alcohol use, toxic substances, autoimmune disease, and metabolic disease. 
• Cirrhosis: marked liver scarring
• Liver cancer
• Hemochromatosis: iron overload
• Wilson disease: copper overload
• Liver ischemia: reduced blood flow to the liver
• Mononucleosis: an infection caused by Epstein-Barr virus
• Diabetes
• Thyroid disease
• Obesity 
• Alcohol
• Medications and supplements, including but not limited to: acetaminophen, amiodarone, antibiotics, fluconazole, methotrexate, nonsteroidal anti-inflammatory drugs (NSAIDs), phenytoin, statins, tricyclic antidepressants, valproate, vitamin A. Always consult with a healthcare provider before starting or stopping any medication.

Low ALT Levels

Low ALT levels are less common than high levels but still require further evaluation and workup. Some studies have indicated that very low ALT levels are associated with advanced aging, frailty, and risk of death. 

Possible causes of low ALT include: 

• Advanced liver disease
• Chronic kidney disease (CKD)
• Malnutrition, such as vitamin B6 deficiency
• Genetic disorders affecting ALT production

ALT and Its Connection to Liver Diseases

Research indicates that ALT is a valuable diagnostic tool for liver disease and is a more specific marker of liver injury than AST. Elevated ALT levels are associated with various liver conditions, including MASLD, viral hepatitis, and drug-induced liver injury. 

Once elevated ALT levels indicate a potential liver issue, your doctor will want to order additional tests and imaging to confirm the abnormal results and identify the underlying cause. These may include:

• Additional liver function blood tests, including albumin, bilirubin, lactate dehydrogenase, and prothrombin time
• Imaging tests, including ultrasound, CT scan, or MRI
• Elastography: a special type of imaging test that uses ultrasound or MRI technology to measure the level of stiffness in the liver
• Endoscopy: a type of endoscopic imaging that allows the doctor to visualize inside the upper gastrointestinal tract and biliary system
• Liver biopsy: a procedure in which a small liver tissue sample is taken to determine the cause of liver disease

AST/ALT Ratio

ALT is often used with other liver function tests to narrow the possible reasons for elevated liver enzymes. 

The AST/ALT ratio is particularly useful in differentiating between types of liver disease. For instance, an AST/ALT ratio greater than 2 suggests alcoholic liver disease, while a ratio less than 1 is more indicative of MASLD.

Managing Liver Diseases Based on ALT Levels

If you have been diagnosed with liver disease, your doctor will discuss disease-specific treatment options to stop disease progression and prevent related health complications. Therapy is often managed by a hepatologist.

Treatment options may include:

• Diet and lifestyle modifications to improve metabolic health 
• Alcohol abstinence
• Antiviral medications
• Immunosuppressive medications
• Cancer therapies
• Copper or iron chelation
• Liver transplant

Repeat liver function tests will be repeated at intervals decided upon by your doctor to monitor treatment efficacy. 

How to Maintain Healthy ALT Levels

While approximately 10% of the population has elevated liver transaminase levels, the good news is that less than 5% of these patients have serious liver disease. This means that treatment for most cases of high ALT levels involves lifestyle changes that support healthy liver function.

Eat a Healthy Diet

Adopting an anti-inflammatory Mediterranean diet has been associated with lowered ALT levels. Specifically, research suggests that the following dietary changes may help improve ALT levels:

• Increase Omega-3 Polyunsaturated Fatty Acids: Incorporate fish oil supplements or foods such as cold-water fish (e.g., salmon, mackerel), flaxseeds, chia seeds, and walnuts into your meals.
• Consume More Folate-Rich Foods: Include leafy greens, asparagus, beans, and fortified cereals to prevent folate deficiency, which has been linked to increased ALT levels in some studies.
• Limit Sugar Intake: Aim to keep sugar consumption to less than 3% of your total daily caloric intake.
• Moderate Coffee Consumption: Drinking one to four cups of coffee daily may have beneficial effects on liver enzymes.

Additionally, abnormal ALT levels have been associated with lower serum antioxidant levels. Antioxidants help neutralize free radicals, which can damage DNA and cause inflammation. Incorporating a variety of colorful fruits and vegetables into your diet ("eating the rainbow") can help increase your intake of dietary antioxidants.

Before making significant changes to your diet, please consult with a healthcare professional or a registered dietitian.

Exercise Regularly

Regular physical activity helps maintain a healthy weight and reduce liver fat content. 

Studies suggest that combining aerobic ("cardio") and resistance ("strength") training in your exercise routine provides the best benefits for patients with MASLD.

Before starting any new exercise program, consult a healthcare professional or certified fitness trainer, especially if you have existing health conditions.

Avoid Toxic Substances

Exposure to heavy alcohol use, cigarette smoke, and environmental chemicals can cause harm to the liver.

To limit exposure to these harmful substances: 

• Moderate Alcohol Consumption: Avoid alcohol altogether or drink in moderation (this means limiting intake to no more than two drinks daily for men or one drink daily for women.
• Quit Smoking: Avoid tobacco use and exposure to second-hand smoke to reduce the risk of liver and other health issues.
• Reduce Exposure to Environmental Toxins: Use an indoor air filter, filter your drinking water, and eat organically-produced foods to reduce exposure to environmental toxins.

Consult with healthcare professionals for personalized advice on reducing exposure to toxic substances.

Milk Thistle

Milk thistle is a popular dietary supplement often used with the intention of supporting liver health. The primary bioactive compounds, including silymarin, in milk thistle are flavonolignans, which are believed to have antioxidative properties and may support the body's inflammatory response.

Some clinical studies suggest that milk thistle supplementation could benefit individuals with certain liver conditions, such as hepatitis and fatty liver disease. Additionally, some research indicates that milk thistle may help improve liver function tests. However, results vary, and more extensive research is necessary to fully understand its efficacy and safety.

Before adding milk thistle or any other supplement to your regimen, consult a healthcare professional, especially if you have existing health conditions or are taking other medications.

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Key Takeaways

• Alanine aminotransferase (ALT) is a liver enzyme that is considered to be a direct marker of liver health. 
• Elevated or reduced ALT levels can signal a range of health conditions, from minor issues to serious liver diseases. Measuring your ALT levels enables early detection and effective management of liver-related conditions. 
• If you have concerns about your liver health, schedule an appointment with your doctor to discuss whether measuring ALT levels would be beneficial in proactively protecting your liver function.