Liver Function Tests: ALT, AST, ALP, and Bilirubin Results Explained
Medically reviewed by Medical Advisory Board Last reviewed 2026-05-13
What elevated liver enzymes mean — patterns, causes, and when to worry
Liver function tests (LFTs) measure enzymes and proteins that reflect liver health. ALT is the most liver-specific marker; AST rises with liver, heart, and muscle damage. The ALT-to-AST ratio, ALP, and bilirubin pattern together distinguish fatty liver from alcohol damage, bile duct disease, and acute hepatitis.
Elevated liver enzymes are one of the most common incidental findings on routine blood work — affecting an estimated 10–20% of the general population, primarily due to the rise in metabolic-associated steatotic liver disease (MASLD, formerly NAFLD). Yet many patients receive a result like 'ALT: 68 U/L (high)' with no explanation of what it means or what to do next.
Liver function tests (LFTs) typically include ALT, AST, ALP, bilirubin, albumin, and total protein — the last four overlap with your CMP. Understanding the pattern of elevation — which enzymes are up, by how much, and their ratio to each other — is more useful than any single number. A 2024 BMJ review established a systematic approach to interpreting these patterns, which we summarize below.
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| Marker | Normal Range | What It Measures | Specificity |
|---|---|---|---|
| ALT (Alanine aminotransferase) | 7 – 56 U/L (optimal: <30 men, <19 women) | Liver cell damage | Most liver-specific |
| AST (Aspartate aminotransferase) | 10 – 40 U/L | Liver, heart, skeletal muscle damage | Less liver-specific (also in muscle) |
| ALP (Alkaline phosphatase) | 44 – 147 U/L | Bile duct obstruction, bone growth | Liver or bone (distinguish with GGT) |
| GGT (Gamma-glutamyl transferase) | 0 – 45 U/L | Bile duct damage, alcohol use | Confirms ALP is liver-origin |
| Bilirubin (total) | 0.1 – 1.2 mg/dL | Hemoglobin breakdown processing | Liver/bile duct/hemolysis |
| Albumin | 3.5 – 5.5 g/dL | Liver synthetic function | Late-stage marker |
Note: Some hepatologists advocate lower ALT cutoffs — <30 U/L for men and <19 U/L for women — as the 'normal' range includes people with undiagnosed fatty liver.
Pattern Recognition: What Your Elevations Mean
Hepatocellular pattern (ALT and AST elevated > ALP):
- Mild elevation (<5× upper limit): Most commonly MASLD/NAFLD (ALT usually > AST), medications (statins, NSAIDs, acetaminophen, supplements), or alcohol. Recheck in 3–6 months after addressing modifiable factors.
- Moderate elevation (5–15× ULN): Acute viral hepatitis (A, B, C), autoimmune hepatitis, drug-induced liver injury, or acute fatty liver.
- Severe elevation (>15× ULN, often >1000 U/L): Acute viral hepatitis, toxin exposure (acetaminophen overdose, mushroom poisoning), ischemic hepatitis (shock liver), or autoimmune flare.
Cholestatic pattern (ALP elevated > ALT/AST):
- Bile duct obstruction (gallstones, tumor), primary biliary cholangitis, primary sclerosing cholangitis, or drug-induced cholestasis. Confirm with GGT — if GGT is normal, elevated ALP is likely bone-origin (growing children, Paget's disease, bone metastases).
AST/ALT ratio clues:
- ALT > AST: Typical of MASLD, metabolic liver disease
- AST > ALT (ratio >2): Alcohol-related liver disease or cirrhosis
- AST > ALT (ratio >1, moderate elevation): Consider muscle damage — CK (creatine kinase) will confirm
Common Causes of Elevated Liver Enzymes
- Metabolic-associated steatotic liver disease (MASLD/NAFLD): Affects ~30% of US adults. The #1 cause of mildly elevated ALT. Driven by insulin resistance, obesity, and metabolic syndrome. See our insulin resistance guide.
- Alcohol: Both acute and chronic. Classic AST:ALT ratio >2 with elevated GGT.
- Medications: Statins (mild ALT elevation in 1–3% of users — usually benign), acetaminophen (dose-dependent), antibiotics, antifungals, anti-seizure drugs, herbal supplements (especially green tea extract, kava).
- Viral hepatitis: Hepatitis B and C can cause chronic low-grade elevation. Screen with Hep B surface antigen and Hep C antibody.
- Intense exercise: Vigorous exercise can transiently elevate AST and ALT for 24–72 hours. If you ran a marathon or did heavy deadlifts before your blood draw, retest after a rest week.
- Hypothyroidism: Can cause mild AST/ALT elevation. Thyroid panel should be checked if liver enzymes are unexplained.
Frequently Asked Questions
What does high ALT mean in a blood test?
High ALT indicates liver cell injury. ALT is the most liver-specific enzyme — when liver cells are damaged or inflamed, ALT leaks into the bloodstream. The most common cause in the US is MASLD (fatty liver disease), affecting ~30% of adults. Medications, alcohol, viral hepatitis, and intense exercise are other common causes. Mild elevations (less than 3 times the upper limit) are usually investigated with lifestyle modifications first, while higher elevations need prompt workup.
What is SGPT in a blood test?
SGPT (serum glutamic-pyruvic transaminase) is the old name for ALT (alanine aminotransferase). They are the same test. Similarly, SGOT is the old name for AST. Some labs, particularly outside the US, still use the SGPT/SGOT terminology. If your report shows SGPT, interpret it exactly as you would ALT.
What level of ALT is dangerous?
ALT levels more than 10 times the upper limit of normal (roughly >500 U/L) indicate significant acute liver injury and warrant urgent evaluation. Levels over 1,000 U/L suggest acute viral hepatitis, toxin exposure (like acetaminophen overdose), or ischemic hepatitis. However, even mild persistent elevation (50-100 U/L) over months deserves investigation, as it may indicate progressive fatty liver disease, chronic hepatitis, or other treatable conditions.
What is AST in a blood test?
AST (aspartate aminotransferase, formerly SGOT) is an enzyme found in liver, heart, and skeletal muscle cells. It rises when any of these tissues are damaged. Unlike ALT, AST is not liver-specific — heavy exercise, a heart attack, or muscle injury can all elevate AST. The ratio of AST to ALT helps distinguish causes: ALT > AST suggests fatty liver, while AST > ALT (especially ratio >2) suggests alcohol-related damage or cirrhosis.
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