LFTs Decoded: What's Actually "Liver" and What Isn't
LFTs Decoded: What's Actually "Liver" and What Isn't The AST/ALT ratio, the hepatocellular vs. cholestatic pattern, and the muscle connection everyone misses. "Liver function tests" is a misnomer that has confused generations of clinicians. Most of the tests in the panel don't measure liver function at all—they measure liver injury . True liver function is reflected by albumin, bilirubin, PT/INR, and the liver's synthetic capacity. The aminotransferases (AST and ALT) tell you about hepatocyte damage, not about how well the liver is doing its job. Let's sort out what each test actually means. The Tests: Injury Markers vs. Function Markers Test What It Measures Key Interpretation ALT (Alanine Aminotransferase) Hepatocyte injury marker. More liver-specific than AST. Elevated in hepatitis (viral, autoimmune, drug-induced, MASLD). The most specific "liver enzyme." AST (Aspartate Aminotransferase) Found in liver AND muscle, heart, kidney...