Aspartate aminotransferase (AST) is a workhorse enzyme that moves amino groups to help cells make and recycle proteins and fuel. It lives inside liver cells, but also in heart and skeletal muscle, kidneys, and red blood cells. When these cells are stressed or damaged, AST leaks into the bloodstream, so it becomes a readout of tissue integrity across multiple systems, not just the liver.In many adults, reference values sit in the teens to low 30s, and a stable mid‑range value generally signals steady-state cell turnover. Men often run slightly higher than women because of greater muscle mass; children and teens can have higher values during growth; healthy pregnancy is usually unchanged or modestly lower.Very low results are usually benign and reflect low release into blood. They can accompany small body or muscle mass, or low vitamin B6 status (AST uses pyridoxal‑phosphate), which may present with fatigue, neuropathy, glossitis, or mild anemia. Rarely, in advanced liver failure with widespread cell loss, AST may fall despite worsening health—typically alongside abnormal bilirubin, albumin, or clotting tests.Higher values indicate recent cell injury. Mild elevations often track with fatty liver, alcohol exposure, medications, or strenuous exercise. Larger rises suggest hepatocellular injury (with fatigue, right‑upper‑quadrant discomfort, dark urine, jaundice), muscle damage or rhabdomyolysis (soreness, weakness, dark urine), or less commonly cardiac ischemia. An AST higher than ALT favors alcohol‑related injury or advanced fibrosis; pairing with CK or LDH helps identify muscle or hemolysis. In pregnancy, elevation raises concern for preeclampsia/HELLP or cholestasis.Big picture: AST bridges amino acid metabolism with organ health. It gains meaning alongside ALT, GGT, ALP, bilirubin, CK, INR, albumin, and platelets, helping map liver, muscle, and metabolic stress that relate to long‑term risks like fibrosis, frailty, and cardiovascular disease.
