ALT Blood Test: What It Means, Normal Range, and High ALT

ALT (alanine aminotransferase) is an enzyme found mostly in your liver. When liver cells are injured or inflamed, they release ALT into the blood — so a high ALT on a blood test is one of the most useful early signals of a liver problem. ALT is usually measured as part of a liver panel (along with AST, ALP, bilirubin, and albumin) and is interpreted together with those results and your history. This guide explains what ALT means, its normal range, what a high or low ALT can indicate, how the AST/ALT pattern helps, and when it's worth seeing a doctor.

Key takeaways

• ALT is a liver enzyme; the blood test reflects how much is leaking from injured liver cells, making it a sensitive marker of liver-cell (hepatocellular) injury.¹
• A typical normal ALT is roughly 7–55 U/L, but the range varies by lab — and many experts now favor lower "healthy" thresholds (about ≤33 U/L for men, ≤25 for women).²
• The most common cause of a mildly high ALT is fatty liver disease (now called MASLD), often linked to weight, blood sugar, and cholesterol.³
• Very high ALT (many times the upper limit) points to acute injury — viral hepatitis, certain medications or toxins, or reduced blood flow.⁴
• ALT is read with AST: the AST/ALT ratio and the pattern of the whole liver panel help point toward the cause.⁴
• A single mildly elevated ALT is common and often benign — but it should be interpreted by a clinician, not in isolation.

What is ALT?

ALT (sometimes written SGPT) is an enzyme concentrated inside liver cells (hepatocytes), where it helps process amino acids. Small amounts circulate in the blood normally. When liver cells are damaged or inflamed, they spill ALT into the bloodstream, raising the measured level. Because ALT is more specific to the liver than AST — which is also found in muscle, heart, and red blood cells — a rise in ALT usually points to the liver itself.¹

ALT is not ordered alone. It comes as part of a comprehensive metabolic panel (CMP) or a dedicated liver (hepatic) panel, which also reports AST, alkaline phosphatase (ALP), bilirubin, and albumin. Reading these together is what gives ALT its meaning: ALT and AST reflect hepatocellular injury, while ALP and bilirubin point more toward bile-flow (cholestatic) problems.⁴

Why is ALT measured?

Clinicians check ALT to:³

• screen for liver problems, often before symptoms appear, in a routine panel;
• investigate symptoms such as fatigue, abdominal pain, nausea, dark urine, or yellowing of the skin and eyes (jaundice);
• monitor known liver conditions, or the effect of medications that can affect the liver;
• assess metabolic health, since elevated liver enzymes often accompany metabolic syndrome and fatty liver disease.⁵

ALT normal range

Units are usually U/L (units per liter). Reference ranges vary between laboratories and methods, so always compare your result to the range printed on your report.² The "right" upper limit is debated: some experts argue the traditional cutoffs are too high and that lower thresholds detect early fatty liver disease sooner.⁶

What a high ALT means

A high ALT signals that liver cells are releasing the enzyme. The degree of elevation helps point toward the cause:¹

• Mild elevation (up to ~5× the upper limit): most often fatty liver disease (MASLD), alcohol, medications (including some over-the-counter drugs and supplements), or chronic viral hepatitis.³
• Marked elevation (10×+ the upper limit): acute injury such as acute viral hepatitis, drug- or toxin-induced liver injury (for example, acetaminophen overdose), or reduced blood flow to the liver (ischemic hepatitis).⁴
• AST/ALT pattern: an AST/ALT ratio > 2 suggests alcohol-related liver disease, while ALT higher than AST is more typical of fatty liver or viral hepatitis. A prolonged INR with a high bilirubin alongside high transaminases signals more urgent, severe injury.⁴

A high ALT is a flag, not a diagnosis. The next step is usually a repeat test plus a targeted work-up: a careful history (alcohol, medications, supplements, metabolic risk factors), viral hepatitis testing, imaging or elastography to look for fat and fibrosis, and noninvasive fibrosis scores such as FIB-4.⁴ Liver biopsy is now used much more selectively.

What a low ALT means

A low ALT is generally not a concern on its own.² Very low levels are occasionally linked to vitamin B6 deficiency (a cofactor the enzyme needs to work) or to frailty in older adults, but a low result by itself rarely needs follow-up. As with all liver tests, the overall pattern and your clinical picture matter far more than a single low number.

What can affect your ALT

Several non-disease factors influence ALT and are worth disclosing:³

• medications and supplements — statins, some antibiotics, acetaminophen, anti-seizure drugs, and certain herbal or "natural" products;
• alcohol in the days before the test;
• intense exercise shortly before testing, which can transiently raise enzymes (especially AST);
• body weight and metabolic health — overweight, high blood sugar, and high triglycerides raise ALT, which is why elevated liver enzymes are common in metabolic syndrome;⁵
• normal biological variation and the lab method, which is why ranges differ between labs.⁶

When to see a doctor

Talk with your clinician if your ALT is above the lab's range — especially if it is persistently elevated, very high, or paired with symptoms such as jaundice, dark urine, abdominal pain, swelling, confusion, or unusual fatigue. Most mildly elevated ALT results are handled with simple steps: a repeat test, a review of medications and alcohol, and an evaluation for fatty liver disease and viral hepatitis, with attention to metabolic risk factors.⁷ A markedly high ALT, or one with a rising bilirubin and abnormal clotting, needs prompt medical attention.

Recent research

According to PubMed, the framework for interpreting ALT has been recently consolidated. A 2026 review in Gastroenterology lays out the modern approach to abnormal liver biochemical tests: ALT and AST reflect hepatocellular injury, evaluation should weight metabolic risk factors, alcohol, medications, and supplements, and noninvasive tools (imaging, elastography, FIB-4) now guide the work-up — with ALT also informing prognosis in cirrhosis and metabolic-associated liver disease.⁴ (Kwo PY et al., Gastroenterology, 2026 — DOI.)

ALT is increasingly read through a metabolic and cardiovascular lens. A 2023 systematic review and meta-analysis (76,000+ people with metabolic syndrome vs. 200,000+ without) found that ALT, AST, and GGT are significantly higher in people with metabolic syndrome.⁵ (Raya-Cano E et al., Diabetology & Metabolic Syndrome, 2023 — DOI.) And a 2025 U.S. population cohort (the Hispanic Community Health Study/Study of Latinos) linked elevated ALT/AST to incident cardiovascular disease and all-cause mortality, particularly in people without diagnosed fatty liver disease.⁸ (Trejo MJ et al., BMC Gastroenterology, 2025 — DOI.)

Get your results interpreted by AI DiagMe

A single liver enzyme like ALT means little alone — its meaning comes from cross-referencing every marker with your full context (AST, ALP, bilirubin, history, medications).

👉 AI DiagMe interprets your lab results — blood, urine, or stool — in plain language, taking your whole profile into account. An informational service that does not provide a diagnosis and complements, never replaces, your physician.

Frequently asked questions

Bottom line

ALT is a liver enzyme and one of the most sensitive blood markers of liver injury. A typical range is about 7–55 U/L (with lower "healthy" thresholds increasingly used). A high ALT most often reflects fatty liver disease, but can signal hepatitis or a medication effect; it is read with AST, the rest of the liver panel, and your history. A low ALT is usually harmless. ALT is a flag, not a diagnosis — your physician interprets it in your full clinical context.

Sources

Official sources and peer-reviewed publications (PubMed) used for this guide: