What are AST and ALT?
AST (Aspartate Aminotransferase) and ALT (Alanine Aminotransferase) are enzymes found primarily in the liver. They are sometimes referred to by their older names, SGOT and SGPT respectively. When liver cells are damaged or inflamed, these enzymes leak into the bloodstream, causing their levels to rise.
ALT is more specific to the liver, while AST is also found in the heart, muscles, kidneys, and brain. Together, they form a key part of the Liver Function Test (LFT) panel and help your doctor assess liver health.
Why is This Test Done?
- To screen for liver disease (hepatitis, fatty liver, cirrhosis)
- To monitor the effects of medications that may affect the liver (statins, anti-TB drugs, anticonvulsants)
- To detect hepatitis B and C infection-related liver damage
- To evaluate alcohol-related liver injury
- To investigate unexplained fatigue, jaundice, or abdominal pain
- To monitor patients with known chronic liver conditions
- As part of a routine health check-up, especially in individuals over 40
How to Prepare for the AST/ALT Test
Simple Preparation
- No special fasting is typically required. However, some laboratories may request fasting if a full liver panel is ordered — check with your doctor.
- Inform your doctor about all medications you are taking, including paracetamol, herbal supplements, and ayurvedic medicines.
- Avoid alcohol for at least 24 hours before the test, as it can temporarily raise liver enzyme levels.
- Avoid strenuous exercise for 24 hours before the test, as intense physical activity can elevate AST.
Understanding Your Results
| Level | AST (U/L) | ALT (U/L) | What It Means |
|---|---|---|---|
| Normal | 10 - 40 U/L | 7 - 56 U/L | Liver is functioning normally. No significant liver cell damage. |
| Mildly Elevated | 40 - 120 U/L | 56 - 170 U/L | Mild liver irritation. Could be due to fatty liver, mild infection, or medication side effects. |
| Moderately Elevated | 120 - 400 U/L | 170 - 500 U/L | Significant liver injury. May indicate active hepatitis, toxic injury, or progressive liver disease. |
| Severely Elevated | Above 400 U/L | Above 500 U/L | Serious liver damage. May be caused by acute hepatitis, paracetamol overdose, or liver failure. Requires urgent medical attention. |
Common Causes of Elevated AST/ALT
- Viral hepatitis (A, B, C, E): One of the most common causes of elevated liver enzymes in Sri Lanka. Hepatitis A and E are linked to contaminated food and water.
- Non-Alcoholic Fatty Liver Disease (NAFLD): Increasingly common due to rising rates of obesity and diabetes. Usually causes mild to moderate ALT elevation.
- Alcohol-related liver disease: Chronic alcohol use damages liver cells. AST is typically higher than ALT in alcoholic liver disease.
- Medications: Paracetamol (acetaminophen) overdose is a leading cause of severe liver damage. Anti-TB drugs (isoniazid, rifampicin), certain antibiotics, and statins can also elevate enzymes.
- Cirrhosis: End-stage scarring of the liver from any chronic cause.
- Autoimmune hepatitis: The body's immune system attacks liver cells.
- Dengue fever: Can cause liver inflammation and elevated AST/ALT, especially in severe dengue.
The AST:ALT Ratio
The ratio of AST to ALT can provide additional diagnostic clues:
- AST:ALT ratio less than 1: Suggests non-alcoholic liver disease, such as viral hepatitis or fatty liver. ALT is typically higher than AST in these conditions.
- AST:ALT ratio greater than 2: Strongly suggests alcoholic liver disease. This is sometimes called the De Ritis ratio.
- AST:ALT ratio greater than 1 (but less than 2): May indicate cirrhosis from any cause, as the liver's ability to produce ALT decreases with advanced scarring.
What Should You Do Next?
- Normal results: No action needed. Continue healthy habits and recheck as recommended by your doctor.
- Mildly elevated: Your doctor may recommend lifestyle changes (reducing alcohol, weight management, reviewing medications) and a repeat test in 4-6 weeks.
- Moderately elevated: Further investigations are usually needed, including hepatitis screening, ultrasound scan of the abdomen, and additional liver function markers.
- Severely elevated: This is urgent. Seek medical attention immediately. Do not delay treatment.
Important: AST and ALT levels alone do not diagnose a specific liver condition. Your doctor will interpret these results alongside your symptoms, medical history, other blood tests, and imaging studies. Never self-diagnose or self-treat based on liver enzyme results alone.