ALT Blood Test: What It Is, How It Works & What Your Results Mean

An ALT blood test (alanine aminotransferase) is one of the most important blood tests for evaluating liver health. It measures the level of ALT enzyme in your blood, which rises when liver cells are damaged or inflamed. Doctors use ALT to screen for liver disease, monitor existing conditions, and evaluate the effects of medications.

What Is an ALT Blood Test?

ALT is an enzyme found primarily inside liver cells. When those cells are injured — from fatty liver disease, alcohol use, hepatitis, or certain medications — ALT leaks into the bloodstream. A simple blood draw can detect this leakage and alert you to liver stress before symptoms become severe.

ALT is more specific to the liver than its counterpart AST, which is also found in the heart, muscles, and other tissues. This makes ALT the preferred first-line screening tool for liver cell damage.

Why Is the ALT Test Important?

Liver disease often causes no symptoms in its early stages. By the time jaundice, fatigue, or abdominal pain appear, significant liver damage may have already occurred. An ALT test can catch liver stress early, when lifestyle changes and treatment are most effective.

Conditions that commonly raise ALT include:

• Non-alcoholic fatty liver disease (NAFLD) — the most common cause in the United States
• Alcoholic liver disease
• Viral hepatitis (A, B, C)
• Medication-induced liver injury — acetaminophen, statins, antibiotics, and herbal supplements
• Autoimmune hepatitis
• Muscle injury — though AST rises more than ALT in this case

How to Prepare for an ALT Blood Test

For a standalone ALT test, fasting is usually not required. You can eat and drink normally before your blood draw. However, if your ALT is being checked as part of a comprehensive metabolic panel (CMP) or liver function panel, your provider may recommend fasting for 8–12 hours to ensure accurate glucose and lipid readings.

Before your test, tell your doctor about:

• All medications and supplements you take
• Recent intense exercise, which can temporarily raise liver enzymes
• Alcohol consumption in the past week
• Any known liver conditions

Understanding Your ALT Results

For most healthy adults, a normal ALT range is approximately 7 to 56 U/L (units per liter). However, "normal" varies by laboratory, age, sex, and body composition.

Even mild elevations deserve attention if they persist. Temporary spikes can occur after strenuous exercise, alcohol use, or certain medications. Persistent elevation warrants further evaluation. See detailed ALT normal ranges by age and gender

What Happens If Your ALT Is High?

A single high ALT result does not mean you have liver disease. Your doctor will consider:

• How high the level is
• Whether it is rising or falling
• Your symptoms and medical history
• Other liver enzymes (AST, ALP, GGT, bilirubin)
• Imaging studies (ultrasound, FibroScan)

If ALT is mildly elevated, repeat testing in 2–4 weeks is often the first step. If it is moderately or severely elevated, additional testing is usually ordered immediately. Learn when to worry about ALT levels

How to Lower ALT Levels

If your ALT is elevated, the most effective interventions are lifestyle changes:

• Lose weight — losing 5–10% of body weight can significantly reduce liver fat and lower ALT
• Reduce sugar and refined carbohydrates — these drive fatty liver more than dietary fat
• Limit or avoid alcohol
• Exercise regularly — both aerobic and resistance training improve liver health
• Review medications — some drugs can raise ALT; never stop a prescription without talking to your doctor

Read our complete guide on lowering ALT naturally

Ordering an ALT Blood Test Online

You can order an ALT blood test directly online without a doctor's referral. After checkout, you will receive a lab requisition that you can take to any participating CLIA-certified lab. Most results are available within 1–2 business days.