Liver Function Tests Explained
Last updated 2026-10-01
What the liver does
Your liver processes nutrients, filters waste, stores energy, and helps blood clot. Because it does so much, its health shows up in several different lab markers. A liver panel groups those markers so they can be read together.
Enzymes that leak from cells
- ALT: fairly specific to the liver. A rise usually points to liver cell irritation.
- AST: found in the liver but also in muscle and other tissue, so it is less specific.
- Alkaline phosphatase (ALP): linked to the bile ducts in the liver and also to bone, so the source depends on context.
- GGT: sometimes added to help confirm whether a raised ALP comes from the liver.
Bilirubin
Bilirubin is a yellow breakdown product from old red blood cells. The liver processes it and sends it out through bile. A rise can come from liver problems, bile duct blockage, or rapid red blood cell breakdown. A mild elevation is sometimes harmless and inherited.
Proteins the liver makes
Albumin and total protein reflect the liver's building work, along with nutrition and other factors. Because they change slowly, they can reveal longstanding issues more than sudden ones.
Reading the pattern
Clinicians look for two broad patterns. When ALT and AST dominate, the problem tends to sit in liver cells. When ALP and bilirubin dominate, a bile duct issue is more likely. The size of the rise matters too, along with symptoms and history. Common contributors include alcohol, medications, fatty liver, viral hepatitis, and muscle injury from intense exercise.
What can move the numbers
- Recent heavy drinking or a new medication.
- Weight and metabolic health.
- Strenuous exercise or muscle injury, which can raise AST.
- Temporary illness or infection.
What to do with a flagged result
A single abnormal enzyme is a clue, not a diagnosis. Clinicians often repeat the test, ask about alcohol and medications, and may add imaging or a hepatitis panel. If you ordered the test yourself, a clinician can help decide whether a repeat or a workup is warranted.
How liver tests are ordered
A liver panel is a standard blood draw and usually needs no fasting, though a clinician may combine it with tests that do. It is often part of a routine check or ordered when there are symptoms such as fatigue, nausea, or abdominal discomfort, or when a medication needs monitoring.
What a mild elevation can mean
A mildly raised enzyme is common and often temporary. Recent exercise, a new medication, alcohol, or a passing illness can move the number. Because these factors come and go, clinicians frequently repeat the panel before drawing conclusions. A repeat under steady conditions tells a clearer story.
Bringing the pieces together
The pattern across enzymes, bilirubin, and proteins matters more than any single value. When one section of the panel is out of step, it can point toward the liver cells or the bile ducts. Imaging or a viral hepatitis panel is sometimes added, but that decision belongs with a clinician.
This article is general information, not medical advice; talk with a clinician about your results.