What a High ALT Level Means

The ALT test measures the amount of alanine transaminase — an enzyme, meaning a protein that speeds up a chemical reaction — in your blood (MedlinePlus, National Library of Medicine, NIH, 2025-01-01).

ALT sits in high concentration inside liver cells. When those cells are injured or inflamed, ALT leaks out into the bloodstream, so the blood level rises. That is why the test is used mainly alongside other liver blood tests to help diagnose and monitor liver disease (MedlinePlus, National Library of Medicine, NIH, 2025-01-01).

The specimen is blood, usually drawn from a vein in the arm, and no special preparation such as fasting is needed beforehand (MedlinePlus, National Library of Medicine, NIH, 2025-01-01). It is often run as part of a panel, so your report may show AST, alkaline phosphatase, bilirubin and albumin next to it — doctors read those together, because an ALT rise is more suggestive of liver disease when other liver values are raised too (MedlinePlus, National Library of Medicine, NIH, 2025-01-01).

One thing worth knowing in advance: a normal ALT does not rule out significant liver disease (American College of Gastroenterology, 2017). The test is a signal, not a verdict.

The severity bands above come from the American College of Gastroenterology (2017). Ranges and upper limits vary between labs and testing methods, and ALT levels are generally higher in males than females (American College of Gastroenterology, 2017). Use the range printed beside your own result, not this table.

Also note: a value flagged "H" can indicate liver injury, but it does not by itself establish that you have a named liver condition.

Listed roughly from the more routine to the less common. All of these push ALT up unless noted.

• Fat in the liver (fatty liver). Widely considered one of the most frequent reasons for a mild ALT rise. There is a linear relationship between ALT and body mass index, and people with a raised BMI plus features of metabolic syndrome — diabetes, overweight or obesity, high lipids, or high blood pressure — and mild ALT elevation are advised to be screened for fatty liver disease with ultrasound (American College of Gastroenterology, 2017).
• Alcohol. Alcohol is among the substances that can be toxic to the liver (MedlinePlus, National Library of Medicine, NIH, 2025-01-01). Women drinking more than 140 g of alcohol per week, or men more than 210 g per week, who have an AST higher than their ALT are considered at risk for alcoholic liver disease (American College of Gastroenterology, 2017).
• Medicines and substances that can injure the liver, including acetaminophen (MedlinePlus, National Library of Medicine, NIH, 2025-01-01). Bring your full list — prescription, over-the-counter and supplements — to your appointment rather than changing anything on your own.
• Viral hepatitis. The CDC recommends one-time hepatitis C testing for people with persistently abnormal ALT levels, and universal one-time screening for all adults 18 and older except in settings where HCV RNA-positivity prevalence is under 0.1% (Centers for Disease Control and Prevention, undated).
• Mononucleosis, a common viral infection that can inflame the liver (MedlinePlus, National Library of Medicine, NIH, 2025-01-01).
• Lab-to-lab and sex differences. Different labs use different upper limits, so the same blood can be flagged high in one report and not another (American College of Gastroenterology, 2017).
• Less common: pancreatitis, hemochromatosis (iron overload), cirrhosis, or death of liver tissue (MedlinePlus, National Library of Medicine, NIH, 2025-01-01).
• Less common: reduced blood flow to the liver (ischemia, "shock liver"), or a liver tumor or cancer (MedlinePlus, National Library of Medicine, NIH, 2025-01-01). Ischemic injury and acetaminophen toxicity are specifically assessed when ALT is more than 15 times the upper limit of normal or above 10,000 IU/L (American College of Gastroenterology, 2017).

1. Read the result next to its own range. Find the printed upper limit of normal on your slip and see how far above it your value sits — borderline, mild or higher changes the pace of what follows.
2. Expect a repeat or clarifying test. Before starting a full evaluation of abnormal liver chemistries, guidelines advise repeating the panel and/or doing a clarifying test to confirm the result is genuinely abnormal (American College of Gastroenterology, 2017).
3. Further testing if it stays up. This commonly means the rest of the liver panel, hepatitis testing — the CDC recommends one-time hepatitis C testing for people with persistently abnormal ALT (Centers for Disease Control and Prevention, undated) — and an ultrasound if fatty liver is being considered (American College of Gastroenterology, 2017).
4. Bring the printed report to the follow-up, along with any earlier liver results you have and a written list of every medicine and supplement you take. Do not rely on remembering the number; the exact value and the lab's range both matter.
5. Agree a plan and a recheck interval. Depending on the cause being considered, that may be monitoring over months, treating an underlying condition, or referral. Immediate referral to a liver specialist is advised for acute hepatitis with a prolonged prothrombin time or encephalopathy — confusion caused by liver failure (American College of Gastroenterology, 2017).
6. Know what cannot wait. Rapid liver injury with prolonged prothrombin time and encephalopathy needs immediate evaluation regardless of the ALT number (American College of Gastroenterology, 2017). Seek care the same day for jaundice, confusion or drowsiness, vomiting you cannot keep fluids down through, or severe upper-right abdominal pain. A single borderline rise with no symptoms can reasonably wait for the scheduled recheck.