ALT Test: Meaning, Function, Normal Ranges, and What Low Levels Mean
The ALT Test (Alanine Aminotransferase Test) is a common blood test that helps doctors check the health of your liver. ALT is an enzyme found mostly in liver cells, and it plays a role in breaking down proteins to produce energy. When the liver is damaged or inflamed, ALT levels usually rise in the blood, which is why this test is very important in liver function evaluation.
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1. What is the ALT Test?
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ALT stands for Alanine Aminotransferase, an enzyme mainly stored in the liver.
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The ALT test measures the amount of this enzyme in your blood.
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Higher levels usually mean liver injury, fatty liver, hepatitis, or alcohol damage.
👉 Example: If someone has hepatitis, their ALT level will likely be very high because the liver cells are leaking ALT into the blood.
2. How Does the ALT Test Work?
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A small blood sample is taken from your arm.
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The lab measures how much ALT enzyme is present.
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The results are compared with normal ranges.
👉 Example: Just like a thermometer shows if you have fever, the ALT test shows if your liver is healthy or not.
3. What Happens if ALT Decreases?
Many people think only high ALT is important, but low ALT also matters.
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Slightly Low ALT: Usually not serious and can happen due to vitamin B6 deficiency or normal variations.
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Very Low ALT: Sometimes linked to liver cirrhosis (advanced liver damage where few cells remain alive) or muscle loss (sarcopenia) in elderly people.
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In most healthy people, low ALT is not dangerous.
👉 Example: If an older person has very low ALT, it may mean their liver cells are no longer working well due to chronic disease.
4. Normal ALT Range for Men, Women, and Children
Different ranges are used depending on age and gender:
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Men: 10 – 40 units per liter (U/L)
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Women: 7 – 35 U/L
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Children: Slightly higher is normal, usually 10 – 45 U/L (because their bodies grow faster).
👉 Example:
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A healthy man may have ALT = 25 U/L → Normal
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A woman with ALT = 37 U/L → Slightly High, needs monitoring
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A child with ALT = 43 U/L → Still Normal for children
5. ALT Test Review & Why It Matters
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High ALT = Warning sign → liver damage (hepatitis, fatty liver, alcohol, medications, obesity).
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Low ALT = Not always serious → may be due to diet, vitamin deficiency, or long-term chronic disease.
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Regular Monitoring is important for people with liver problems, diabetes, obesity, or those taking medications that affect the liver.
✅ Final Words for Blog Readers:
The ALT test is a simple but powerful tool to check liver health. Always discuss your results with a doctor because ALT alone doesn’t tell the full story—it should be reviewed with other tests like AST, ALP, and Bilirubin.