How to Understand a Liver Function Test (LFT) Report

What Does a Liver Function Test (LFT) Measure?

The liver is the body's primary biochemical laboratory, performing over 500 vital functions—including filtering metabolic toxins, synthesizing critical blood-clotting proteins, regulating cholesterol, and producing bile to digest dietary fats.

A Liver Function Test (LFT)—more accurately described as a hepatic biochemical panel—measures specific enzymes, proteins, and pigments circulating in your blood. Rather than assessing a single variable, clinicians examine the pattern and ratio of these biomarkers to determine whether a concern originates from liver cell injury (hepatocellular), bile duct obstruction (cholestatic), or reduced protein production (synthetic).

1. Liver Enzymes: ALT (SGPT) and AST (SGOT)

When liver cells (hepatocytes) undergo stress, inflammation, or injury, their outer membranes become permeable, leaking internal enzymes into the bloodstream:

• ALT (Alanine Aminotransferase / SGPT):
  • Standard Adult Range: Approximately 7 to 56 units per liter (U/L) (varies by laboratory and biological sex).
  • Clinical Significance: ALT is concentrated predominantly within liver cells, making it a highly specific indicator of hepatic inflammation. Common triggers for mild to moderate elevations include non-alcoholic fatty liver disease (NAFLD/MASLD), viral hepatitis, alcohol consumption, and certain prescription medications (such as statins or NSAIDs).
• AST (Aspartate Aminotransferase / SGOT):
  • Standard Adult Range: Approximately 10 to 40 U/L.
  • Clinical Significance: AST is present in liver cells, but also abundantly in cardiac muscle, skeletal muscle, kidneys, and brain tissue. Elevated AST alongside normal ALT frequently points to non-hepatic origins (such as strenuous weight training, muscle injury, or hemolysis).
• The AST/ALT Ratio:
  • An AST/ALT ratio under 1 is typical in viral hepatitis and non-alcoholic fatty liver disease.
  • An AST/ALT ratio greater than 2 is characteristic of alcohol-induced liver inflammation, although it can also appear in advanced cirrhosis.

2. Cholestatic Markers: ALP and GGT

These enzymes assess the integrity of your biliary drainage system (the network of bile ducts transporting digestive bile from the liver to the gallbladder and small intestine):

• Alkaline Phosphatase (ALP):
  • Context: Found in bile duct lining cells, but also in bone, intestine, and placenta during pregnancy.
  • Elevated ALP: When markedly elevated alongside high GGT (Gamma-Glutamyl Transferase), it strongly suggests biliary blockage (such as gallstones or biliary duct narrowing). High ALP with normal GGT often originates from bone remodeling or adolescent growth spurts.

3. Bilirubin Fractions

Bilirubin is a yellowish-orange pigment produced during the normal breakdown of aged red blood cells. The liver processes (conjugates) bilirubin so it can be excreted in bile:

• Total Bilirubin: Normal range is typically 0.2 to 1.2 mg/dL. Values exceeding 2.5 to 3.0 mg/dL lead to noticeable jaundice (yellowing of sclera and skin).
• Direct (Conjugated) Bilirubin: Bilirubin that has been processed by liver cells. High direct bilirubin implies impaired bile outflow into the digestive tract.
• Indirect (Unconjugated) Bilirubin: Bilirubin bound to albumin prior to hepatic processing. High indirect bilirubin with normal ALT/AST is commonly seen in Gilbert's syndrome—a benign, inherited condition where bilirubin clearance slows during fasting, dehydration, or physical stress.

High-Yield Questions to Ask Your Doctor

When discussing your LFT report with your physician, consider asking:

1. "Does the pattern suggest hepatocellular inflammation (high ALT/AST) or biliary restriction (high ALP/bilirubin)?"
2. "Could any of my current daily medications, vitamins, or fitness routines be contributing to this elevation?"
3. "Should we schedule an abdominal ultrasound to evaluate liver echogenicity and rule out gallstones?"
4. "Do we need repeat testing in 6 to 12 weeks to determine if this is an acute transient fluctuation or a persistent trend?"