Liver Function Tests: What ALT, AST, GGT, and Bilirubin Show
Order ALT Blood Test (SGPT) for LiverQuick Answer
Liver function tests catch liver irritation early, often before symptoms appear. This guide explains each marker, normal ranges, and how to order a liver panel.
Key Takeaways
- Liver function tests measure enzymes and proteins that show liver injury and function.
- A standard liver panel includes ALT, AST, ALP, GGT, bilirubin, albumin, and total protein.
- Typical adult ranges are about 7 to 56 U/L for ALT and 10 to 40 U/L for AST.
- Total bilirubin normally runs about 0.1 to 1.2 mg/dL in adults.
- Fatty liver, viral hepatitis, alcohol, and medicines are common causes of high liver enzymes.
- Fasting for 8 to 12 hours is often requested before a liver or metabolic panel.
What Are Liver Function Tests?
Liver function tests (LFTs) are a group of blood tests that show how well the liver is working and whether liver cells are irritated or damaged. The liver filters blood, processes medicines and alcohol, makes bile for digestion, stores energy, and produces proteins for clotting. Because liver disease often causes no symptoms until it is advanced, blood testing is the main way problems are caught early.
A standard liver panel measures enzymes that leak from injured liver cells, plus bilirubin and proteins that reflect how well the liver is doing its manufacturing jobs. Results are interpreted as patterns across markers rather than single numbers, and mildly abnormal values are commonly rechecked before any conclusions are drawn.
Which Markers Are Included
A typical liver panel includes the following markers. This guide is educational information, not medical advice.
| Marker | What it shows |
|---|---|
| ALT (alanine aminotransferase) | Enzyme most specific to liver cells; rises with liver injury |
| AST (aspartate aminotransferase) | Enzyme in liver, heart, and muscle; read together with ALT |
| ALP (alkaline phosphatase) | Enzyme related to bile ducts and bone; rises with bile blockage |
| GGT (gamma-glutamyl transferase) | Enzyme sensitive to bile duct irritation and alcohol use |
| Bilirubin | Breakdown product of red cells the liver clears; high levels cause jaundice |
| Albumin and total protein | Proteins the liver manufactures; low levels suggest reduced liver capacity |
GGT is often ordered alongside the panel to sort out whether a raised ALP comes from the liver or bone. Ammonia is a separate test reserved for specific situations such as confusion in advanced liver disease.
Normal Ranges for Liver Markers
Reference ranges vary by laboratory, sex, and age, so always use the range on your own report. Typical adult ranges used by many laboratories include:
| Marker | Typical adult reference range |
|---|---|
| ALT | About 7 to 56 U/L |
| AST | About 10 to 40 U/L |
| ALP | About 44 to 147 U/L |
| GGT | About 9 to 48 U/L |
| Total bilirubin | About 0.1 to 1.2 mg/dL |
| Albumin | About 3.5 to 5.5 g/dL |
Strenuous exercise, alcohol, many prescription and over-the-counter medicines, and herbal supplements can all raise liver enzymes temporarily. Tell the lab what you take so results can be read in context.
What Abnormal Patterns May Suggest
- ALT much higher than AST often points to liver cell injury from causes such as fatty liver, viral hepatitis, medicines, or alcohol.
- AST much higher than ALT can point to alcohol-related injury but also to muscle or heart sources, since AST is less liver-specific.
- High ALP with high GGT often points to bile duct irritation or blockage, including gallstones.
- High ALP with normal GGT may point to a bone rather than liver source.
- High bilirubin with jaundice (yellowing of skin or eyes), dark urine, or pale stools calls for prompt medical evaluation.
- Low albumin with prolonged clotting times can suggest reduced liver manufacturing capacity in chronic disease.
Only a clinician can diagnose liver disease. A single mildly raised enzyme after exercise, alcohol, or a new medicine is usually rechecked rather than acted on immediately.
How to Order Liver Function Tests and Where to Get Tested
Direct-access lab testing lets you order liver function tests online without a doctor visit. Choose a hepatic function panel, a comprehensive metabolic panel (which includes liver markers plus kidney and electrolyte markers), or individual markers such as ALT or GGT. After checkout you receive a lab requisition by email and visit a local collection site for a standard blood draw with a photo ID.
Fasting for about 8 to 12 hours is often requested, especially when the liver panel is bundled into a metabolic panel. Avoid alcohol for at least 24 hours before the draw and tell the lab about all medicines and supplements. Results are typically available within one to two business days.
How Much Do Liver Function Tests Cost?
A hepatic function panel commonly costs about $29 to $69 through direct-access labs. A comprehensive metabolic panel with liver markers typically runs about $29 to $59, while individual markers such as ALT or GGT cost about $19 to $49 each. Prices vary by laboratory and city, with a possible small collection fee at the draw site.
Because no insurance claim is filed, the checkout price is generally the full price. A bundled panel is usually better value than single markers when the cause of abnormal liver enzymes is still unknown.
Frequently Asked Questions
What is included in liver function tests?
A liver panel usually includes ALT, AST, ALP, GGT, bilirubin, albumin, and total protein. Each marker reflects a different aspect of liver health.
What are normal ALT and AST levels?
Typical adult ranges are about 7 to 56 U/L for ALT, 10 to 40 U/L for AST, and 0.1 to 1.2 mg/dL for total bilirubin, but ranges vary by laboratory.
What causes high liver enzymes?
Fatty liver, viral hepatitis, alcohol, medicines, and supplements are common causes. Strenuous exercise can also raise enzymes temporarily.
Do I need to fast for liver function tests?
Fasting for 8 to 12 hours is often requested, especially in a metabolic panel. Avoid alcohol for 24 hours before the draw.
Can I order liver function tests without a doctor?
Yes. Direct-access lab testing lets you order a hepatic panel, a comprehensive metabolic panel, or single markers online and visit a local collection site.
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This guide is reviewed for sourcing accuracy against the references listed above. It is educational information, not medical advice. Always consult a qualified healthcare provider about your own results and care.
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Order ALT Blood Test (SGPT) for LiverReviewed by the LabAppointments Editorial Team
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