Alanine Aminotransferase (ALT)

What it is

Alanine aminotransferase, often shortened to ALT, is an enzyme found mainly in your liver. Enzymes are like tiny helpers in your body that speed up chemical reactions. ALT plays a role in processing protein, helping to convert one type of amino acid (alanine) into another. It's also found in smaller amounts in other organs like your kidneys, heart, and muscles.

When liver cells (called hepatocytes) are healthy, they keep most of the ALT inside. However, if these liver cells become damaged or inflamed, they can release more ALT into your bloodstream. This is why a blood test measuring ALT levels is often used as an indicator of liver health.

The typical reference range for ALT in the UK for adults is generally up to 40 Units per litre (U/l). However, it's important to remember that laboratory reference ranges can vary slightly, and what's considered normal can also depend on factors like age and sex.

Why it matters

Because ALT is primarily found in the liver, a higher-than-normal level in your blood can suggest that your liver might be experiencing some stress or damage. Think of it like a smoke alarm; when the alarm goes off, it doesn't tell you exactly what's burning, but it signals that there might be a fire somewhere. Similarly, an elevated ALT level signals that something might be affecting your liver.

A persistently high ALT level could be a sign of various liver conditions, some of which might need medical attention. It's a useful marker for doctors to monitor the health of your liver over time, especially if you have a known liver condition or risk factors for liver disease. It can also help doctors track how well a treatment for a liver condition is working.

On the other hand, very low levels of ALT are not usually a cause for concern, as they don't typically indicate a problem.

What can cause it to be high or low

Several factors can lead to an increase in ALT levels. The most common reason is damage to liver cells. This damage can be caused by:

• Viral hepatitis: Infections like Hepatitis A, B, and C can cause inflammation of the liver.
• Alcoholic liver disease: Heavy or long-term alcohol consumption can damage liver cells.
• Non-alcoholic fatty liver disease (NAFLD): This is a condition where excess fat builds up in the liver, which can lead to inflammation and damage. It's often associated with obesity, diabetes, and high cholesterol.
• Medications: Certain medicines, including some statins, antibiotics, and painkillers, can sometimes affect the liver and raise ALT levels. It's important to tell your doctor about all medications you are taking.
• Other liver conditions: Conditions like autoimmune hepatitis, Wilson's disease, or haemochromatosis can also impact liver health.
• Muscle injury: While less common, significant muscle damage from strenuous exercise or injury can also release ALT, as it's present in muscle tissue too.
• Coeliac disease: In some individuals with undiagnosed coeliac disease, elevated ALT levels can be seen.

Very rarely, extremely low ALT levels might be associated with certain deficiencies, but this is not typically something that is monitored or a cause for concern in routine blood tests.

Lifestyle factors that may help

If your ALT levels are elevated due to lifestyle-related factors, making certain changes could potentially help improve your liver health. These are topics you might wish to discuss with your GP:

• Diet: Focusing on a balanced diet rich in fruits, vegetables, and whole grains, while limiting processed foods, sugary drinks, and excessive saturated fats, can be beneficial for overall health and liver function.
• Weight management: If you are overweight or obese, achieving and maintaining a healthy weight can significantly reduce the strain on your liver, particularly in cases of fatty liver disease.
• Alcohol intake: Reducing or moderating alcohol consumption is crucial if your liver health is being affected by alcohol.
• Exercise: Regular physical activity can help with weight management and improve insulin sensitivity, both of which are important for liver health.
• Medication review: If certain medications are suspected of affecting your ALT levels, discussing alternatives with your doctor is important.

Questions to discuss with your GP

If you've had an ALT blood test, or if you're concerned about your liver health, here are some questions you might want to consider discussing with your GP:

• What does my ALT result mean in the context of my overall health?
• Are there any specific lifestyle changes that would be most beneficial for me based on my results?
• Are there any other tests that might be helpful to understand the cause of any changes in my ALT level?
• Could any of the medications or supplements I'm currently taking be affecting my ALT level?
• What are the potential long-term implications of my current ALT level?
• How often should my ALT levels be monitored in the future?