ALT (Alanine Aminotransferase)
Everything you need to know about ALT (Alanine Aminotransferase) levels, including what normal ranges look like and what abnormal results might indicate.
Standard Reference Range
Unit: U/LReference ranges may vary slightly between laboratories. Always consult your doctor for interpretation.
What is ALT?
Alanine Aminotransferase (ALT) is an enzyme found primarily in your liver cells. Think of it as a worker inside the liver factory. When the factory (liver) is running smoothly, the workers stay inside. However, if the factory walls are damaged (liver cell injury), the workers leak out into the street (bloodstream).
Therefore, measuring the amount of ALT in your blood gives doctors a direct clue about liver damage.
Key Takeaway
ALT is considered the most specific marker for liver injury. While other enzymes like AST can come from the heart or muscles, ALT is almost exclusively from the liver.
Why is this test performed?
Your doctor might order an ALT test as part of a routine checkup (Comprehensive Metabolic Panel) or if you have symptoms of liver issues, such as:
- Jaundice: Yellowing of the skin or eyes.
- Abdominal Pain: Specifically in the upper right side.
- Dark Urine: Tea-colored urine.
- Nausea or Vomiting: Unexplained digestive issues.
- Fatigue: Chronic tiredness.
It is also used to monitor:
- Progression of known liver diseases (e.g., Hepatitis, Fatty Liver).
- Side effects of medications that can affect the liver (e.g., cholesterol drugs, long-term painkiller use).
Interpreting Your Results
High Levels (Elevated ALT)
High ALT levels indicate that liver cells are being damaged or inflamed. The degree of elevation often hints at the cause.
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Mild Elevation (2-3x normal):
- Fatty Liver Disease (NAFLD): Very common, often linked to diet and weight.
- Alcohol Consumption: Regular or binge drinking.
- Medications: Statins, antibiotics, or over-the-counter pain relievers (Tylenol/Paracetamol).
- Chronic Hepatitis B or C.
-
Moderate to High Elevation (10-20x normal):
- Acute Hepatitis: Viral infection (Hep A, B, C).
- Alcoholic Hepatitis: Severe inflammation from alcohol.
-
Very High Elevation (＞50x normal):
- Drug Overdose: Specifically Acetaminophen (Tylenol) toxicity.
- Ischemic Liver: "Shock liver" caused by very low blood pressure or heart failure.
Don't Panic
A mildly elevated ALT is a very common finding and often resolves on its own. Stress, strenuous exercise, or even a recent viral cold can cause a temporary spike.
Low Levels
Low ALT levels are generally not a cause for concern and are considered normal. In rare cases, extremely low levels might be linked to Vitamin B6 deficiency or chronic kidney disease, but this is clinically uncommon.
For Professionals: Clinical Nuances
The AST/ALT Ratio (De Ritis Ratio)
The ratio of AST to ALT can provide differential diagnostic value:
- Ratio ＞ 2:1 (AST is double ALT): Highly suggestive of Alcoholic Liver Disease.
- Ratio ＜ 1 (ALT is higher than AST): More typical of Non-Alcoholic Fatty Liver Disease (NAFLD) or Viral Hepatitis.
Interfering Factors
- Exercise: Intense weightlifting or marathon running can release muscle enzymes, causing a transient rise in ALT (and a massive rise in AST/CK).
- Time of Day: ALT levels can exhibit diurnal variation, often lower in the morning and higher in the afternoon.
- Hemolysis: Ruptured red blood cells in the sample can falsely elevate results.
Frequently Asked Questions
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