ALT Blood Test (Alanine Aminotransferase)
The ALT blood test measures alanine aminotransferase, an enzyme found mostly in liver cells. It is one of the most frequently ordered blood tests in routine care, usually read alongside related markers rather than on its own, and it is a standard part of many liver-focused panels.
About this test
ALT is an enzyme that does its everyday work inside cells, with the liver holding the largest share. When liver cells are stressed or damaged, some of their contents, including ALT, appear in the bloodstream in larger amounts.
A clinician reading an ALT result rarely looks at the number in isolation. It is usually considered together with AST, another enzyme with a similar story, and often with other liver-associated markers.
Who might consider this test?
- As with any laboratory result, interpretation belongs with a licensed clinician who knows your history.
Test details
| Quest code | 823 |
|---|---|
| Methodology | Spectrophotometry |
| Sample type | 1 mL serum |
| Collection | Quest patient service center |
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Quest resources
Additional details
Why ALT is so closely tied to the liver
Every organ uses enzymes, but ALT is concentrated in liver tissue more than anywhere else in the body. That concentration is what makes it a useful signal: meaningful shifts in blood levels of ALT tend to track with what is happening to liver cells. Other tissues contribute small amounts, which is one of several reasons a single reading is never treated as a verdict.
Because the liver has many day-to-day responsibilities — processing nutrients, medications, and much of what passes through the digestive tract — ALT is often watched over time rather than judged once.
ALT and AST are usually read together
AST is a related enzyme that overlaps with ALT but is less specific to the liver, appearing in muscle and other tissues as well. Clinicians commonly consider the two side by side, because the relationship between them can suggest which tissue is contributing and how the picture is evolving. Ordering them together, or as part of a liver-focused panel, is routine practice.
What can influence an ALT result
ALT can move with many ordinary circumstances — recent strenuous exercise, some medications and supplements, alcohol, and body-weight changes among them. That sensitivity is part of what makes it informative, and also why an unexpected result usually leads to a conversation and often a repeat test rather than an immediate conclusion.
Order online and a physician order is included — no doctor's visit and no insurance needed. Your sample is collected at a Quest Diagnostics patient service center.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What is ALT in a blood test?
ALT (alanine aminotransferase) is an enzyme found mostly in liver cells. The blood test measures how much of it is circulating, which is why it is closely associated with liver health on lab reports.
Why is ALT usually tested with AST?
AST is a related enzyme found in the liver and other tissues. Reading the two together gives a clinician more context than either one alone, so they are commonly ordered side by side.
Can everyday things affect an ALT result?
Yes. Strenuous exercise, alcohol, some medications and supplements, and other ordinary factors can influence a result, which is one reason clinicians often repeat the test before drawing conclusions.
Do I need to fast before an ALT test?
ALT itself does not generally require fasting, but it is often drawn as part of a panel that does. Follow the preparation instructions on your requisition.
Does a changed ALT result mean liver disease?
No single result establishes a condition. ALT is a signal that a clinician interprets alongside other markers, your history, and often a repeat measurement.
How much is a ALT test?
$15, paid once at checkout. The price includes the physician's order this test requires and sample collection at a Quest patient service center.