Liver Function Tests (LFTs): Normal Ranges Explained

What Are Liver Function Tests?

Liver function tests (LFTs), also called a liver panel, are a group of blood tests that provide information about your liver's health. Despite the name, these tests don't actually measure how well your liver functions—most measure enzymes that leak out of liver cells when they're damaged.

Think of your liver as a chemical processing plant. It:

• Filters toxins from your blood
• Produces bile for digestion
• Makes proteins (albumin, clotting factors)
• Stores energy (glycogen)
• Metabolizes medications and alcohol

When the liver is injured or stressed, liver cells (hepatocytes) leak enzymes into the bloodstream. LFTs measure these enzymes, allowing doctors to detect liver damage early.

What LFTs typically include:

• ALT (Alanine Aminotransferase): Liver-specific enzyme
• AST (Aspartate Aminotransferase): Enzyme from liver, muscle, heart
• ALP (Alkaline Phosphatase): Enzyme from liver and bone
• Bilirubin: Waste product from red blood cell breakdown
• Albumin: Protein made by the liver
• Total Protein: Measures total protein in blood

Understanding Your Results

ALT (Alanine Aminotransferase)

What it measures: Enzyme found primarily in liver cells

Normal range: 7-56 U/L (varies by lab)

What it means: ALT is the most liver-specific enzyme. When ALT is elevated, it indicates liver cell injury.

AST (Aspartate Aminotransferase)

What it measures: Enzyme found in liver, heart, muscle, kidneys, brain

Normal range: 10-40 U/L

What it means: AST is less liver-specific than ALT. It's elevated in liver disease but also in muscle injury and heart attacks.

AST:ALT ratio: Comparing AST to ALT helps identify the cause:

• ALT ＞ AST: Non-alcoholic liver disease (fatty liver, viral hepatitis)
• AST ＞ ALT (ratio ＞2:1): Alcoholic liver disease, cirrhosis
• AST ＞＞ ALT: Muscle injury, heart attack

ALP (Alkaline Phosphatase)

What it measures: Enzyme from liver (bile ducts) and bone

Normal range: 44-147 U/L

What it means: ALP elevation patterns help identify the problem:

• ALP elevated with normal ALT/AST: Bile duct obstruction, bone disease
• ALP elevated with high ALT/AST: Liver cell injury + bile duct involvement

Causes of elevated ALP:

• Liver: Bile duct obstruction (gallstones, tumors), primary biliary cholangitis
• Bone: Paget's disease, bone metastases, healing fractures, pregnancy
• Other: Hyperthyroidism, certain medications

Bilirubin

What it measures: Breakdown product of red blood cells

Normal range: 0.3-1.2 mg/dL

What it means: Elevated bilirubin causes jaundice (yellowing of skin/eyes).

Types of bilirubin elevation:

• Direct (conjugated) bilirubin elevated: Bile duct obstruction, liver dysfunction
• Indirect (unconjugated) bilirubin elevated: Hemolysis (red blood cell breakdown), Gilbert's syndrome (benign)

Albumin

What it measures: Protein made by the liver

Normal range: 3.5-5.0 g/dL

What it means: Low albumin suggests the liver isn't synthesizing proteins adequately.

Causes of low albumin:

• Liver disease (especially cirrhosis)
• Malnutrition, protein deficiency
• Kidney disease (protein loss in urine)
• Inflammation (albumin is a negative acute phase reactant)
• Chronic illness

Total Protein

What it measures: Albumin + globulins

Normal range: 6.3-7.9 g/dL

What it means: Low total protein suggests malnutrition, liver disease, or kidney disease. High total protein suggests dehydration or chronic inflammation.

Patterns of Liver Test Abnormalities

The pattern of enzyme elevations helps identify the cause:

Hepatocellular pattern (liver cell injury):

• ALT and AST significantly elevated
• ALP normal or mildly elevated
• Causes: Viral hepatitis, toxic liver injury, ischemic hepatitis, autoimmune hepatitis

Cholestatic pattern (bile duct obstruction):

• ALP significantly elevated (often ＞3x upper limit)
• GGT significantly elevated
• ALT and AST normal or mildly elevated
• Bilirubin often elevated
• Causes: Gallstones, bile duct strictures, tumors, primary biliary cholangitis

Mixed pattern:

• Both ALT/AST and ALP elevated
• Causes: Drug-induced liver injury, advanced liver disease, infiltrative diseases

When Are Liver Function Tests Ordered?

Your Action Plan Based on Results

If all LFTs are normal:

• Continue healthy lifestyle
• No specific liver follow-up needed
• Routine screening as recommended
• Limit alcohol consumption
• Maintain healthy weight

If you have mild elevations (＜2x upper limit):

• Repeat testing in 2-3 months to confirm
• Review all medications and supplements with your doctor
• Stop alcohol temporarily
• If overweight, weight loss may normalize enzymes
• Screen for metabolic syndrome (diabetes, cholesterol, blood pressure)
• If elevation persists, further evaluation (ultrasound, viral hepatitis testing) may be needed

If you have moderate elevations (2-5x upper limit):

• Repeat testing promptly
• Comprehensive evaluation needed:
  • Viral hepatitis testing
  • Metabolic screening
  • Medication review
  • Ultrasound imaging
  • Iron studies (hemochromatosis)
  • Autoimmune markers if indicated
• Treatment depends on cause

If you have marked elevations (＞5x upper limit):

• Urgent evaluation needed
• May indicate acute liver injury
• Hospitalization if symptomatic or bilirubin elevated
• Comprehensive workup to identify cause
• Stop potential offending medications

Common Causes of Elevated Liver Enzymes

Fatty liver disease (NAFLD/NASH):

• Most common cause of mild enzyme elevation
• Associated with obesity, diabetes, metabolic syndrome
• Weight loss (5-10% body weight) often normalizes enzymes
• Usually benign but can progress to cirrhosis in some cases

Medication-induced liver injury:

• Many medications can elevate enzymes
• Usually resolves when medication stopped
• Common culprits: statins, antibiotics, NSAIDs, antifungals
• Herbal supplements can also cause liver injury

Alcohol-related liver disease:

• Pattern: AST ＞ ALT (ratio ＞2:1), GGT elevated
• Enzyme elevation usually modest (ALT ＜300 U/L)
• Abstinence often improves enzymes
• Continued drinking can progress to cirrhosis

Viral hepatitis:

• Hepatitis B and C can cause marked enzyme elevation
• Chronic infection can cause persistent mild-moderate elevation
• Treatment available for both viruses
• Vaccination prevents hepatitis B

Autoimmune hepatitis:

• Immune system attacks liver
• More common in women
• Can cause severe elevation
• Treated with immunosuppressants

Common Questions

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Disclaimer: This information is for educational purposes only and does not constitute medical advice. Always consult your healthcare provider to interpret your liver function test results and determine appropriate management.