Key Benefits

• Check liver cell health by measuring ALT, a liver enzyme in blood.
• Spot early liver stress from fatty liver, alcohol, medications, or viral hepatitis.
• Clarify unexplained fatigue, nausea, or right-upper abdominal pain as liver-related.
• Guide treatment choices and monitoring for hepatitis, fatty liver, or autoimmune disease.
• Protect medication safety by flagging drug-induced liver injury early.
• Support pregnancy care by checking liver stress in preeclampsia, HELLP, or cholestasis.
• Track recovery by trending ALT after weight loss, alcohol reduction, or treatment.
• Best interpreted with AST, alkaline phosphatase, bilirubin, and your symptoms.

What is Alanine Aminotransferase (ALT)?

Alanine aminotransferase (ALT) is an enzyme found mainly in liver cells (hepatocytes). Enzymes accelerate chemical reactions; ALT specifically swaps an amino group between molecules (a transaminase). It sits in the fluid part of the cell (cytosol) and is produced largely by the liver, with smaller amounts present in skeletal muscle, heart, and kidney. In its day-to-day job, ALT transfers an amino group from the amino acid alanine to a partner molecule, forming pyruvate and glutamate—basic building blocks used for energy and nitrogen handling.

ALT’s main significance is in how it supports energy flow and nitrogen balance and what it reveals about liver cells. By turning alanine into pyruvate, ALT feeds the liver’s glucose-making pathway during fasting (gluconeogenesis) and helps shuttle nitrogen safely from muscle to liver (the glucose–alanine cycle). Because ALT is concentrated in hepatocytes, changes in ALT found in blood primarily reflect the condition of these cells—their integrity and metabolic strain—making ALT a practical lens on liver cell activity and the body’s processing of amino acids.

Why is Alanine Aminotransferase (ALT) important?

Alanine aminotransferase (ALT) is a liver-cell enzyme that quietly reports how intact your hepatocytes are. Because the liver orchestrates energy use, detoxification, bile production, clotting factor synthesis, and hormone metabolism, shifts in ALT give a window into whole‑body metabolic and inflammatory stress.

In steady health, ALT sits low and stable, typically in the lower-to-middle part of the lab’s reference interval. Women usually have slightly lower reference limits than men, and children/teens have age- and sex-specific cutoffs. When ALT is on the low side, it often has no clinical consequence. It can reflect limited availability of its cofactor vitamin B6, reduced liver cell mass in advanced cirrhosis, or low muscle mass and frailty in older adults; symptoms, if present, come from those conditions (e.g., weakness, neuropathic tingling, easy fatigue), not from the enzyme itself. Low values in pregnancy are not concerning.

When ALT rises, hepatocytes are leaking enzyme into blood. Mild, persistent increases commonly accompany fatty liver related to insulin resistance; higher levels may occur with viral hepatitis, medication or toxin injury, ischemia, or alcohol use (often with AST higher than ALT). Muscle injury and strenuous exercise can contribute small bumps. Many people feel nothing; others notice fatigue, right‑upper‑abdominal discomfort, nausea, dark urine, itch, or jaundice as bile handling and metabolism are disrupted. In pregnancy, any elevation deserves attention because it can signal disorders such as preeclampsia-related liver involvement or intrahepatic cholestasis. In children and teens, sustained elevation often points to fatty liver in the setting of excess weight.

Big picture: ALT is a sensitive barometer of hepatocellular stress and metabolic load. Interpreted with AST, alkaline phosphatase, GGT, bilirubin, albumin, and clotting measures, it helps gauge risk for fibrosis, cirrhosis, and hepatocellular carcinoma, and it tracks with future diabetes and cardiovascular risk, while very low levels in elders can reflect frailty.

What Insights Will I Get?

Alanine aminotransferase (ALT) is a liver enzyme that shuttles amino groups to make glucose from amino acids (transamination). It mostly lives inside hepatocytes, so blood levels reflect how “leaky” or stressed those cells are. Because the liver is central to energy processing, lipid handling, detoxification, and hormone metabolism, ALT tracks with whole‑body metabolic load and cardiometabolic risk.

Low values usually reflect minimal hepatocyte leakage and can be a sign of low inflammatory and metabolic stress. In older adults, very low ALT may correlate with low muscle mass and frailty (sarcopenia), since ALT is also present in muscle, but it is rarely a concern by itself. Pregnancy does not meaningfully lower ALT beyond assay variation.

Being in range suggests intact liver cell membranes and balanced glucose–lipid metabolism. Within the reference interval, risk for metabolic syndrome and cardiovascular disease tends to be lowest toward the low-to-mid portion rather than the high end, assuming other liver tests are normal.

High values usually reflect hepatocellular injury or metabolic overload. Common drivers include fat accumulation in the liver (metabolic dysfunction–associated steatotic liver disease), insulin resistance, viral hepatitis, alcohol-related injury, medication or toxin effects, and sometimes muscle injury. Males often have slightly higher baselines than females. In pregnancy, elevated ALT is notable because it can signal pregnancy‑specific liver conditions. In older adults, even modest increases may be meaningful.

Notes: ALT can rise transiently after strenuous exercise or intramuscular injury and varies with body size and age. Numerous drugs and supplements affect it. Assays differ slightly across labs. Interpreting ALT alongside AST, GGT, bilirubin, and clinical context strengthens its meaning.