The six markers are three families. ALT and AST are enzymes inside liver cells that leak when cells are damaged, so the level is roughly how much got hit; ALT is liver-specific, while AST also comes from muscle, so a high AST alone can be a hard workout rather than your liver ¹. ALP and GGT rise when bile can't flow out, blocked plumbing rather than damaged cells; ALP also comes from bone, so a normal GGT beside a high ALP points at bone ². Bilirubin and albumin are the only two that measure what the liver does: waste it should clear, and a protein it should make. A low albumin means the factory is failing, and because it moves slowly, it signals chronic disease ³.

Almost every abnormal panel sorts into one of three pictures. Liver-cell injury, blocked bile flow, or an isolated bilirubin bump. Within injury, the size of the ALT rise narrows the cause: above roughly 500 IU/L almost always means acute viral hepatitis, an acetaminophen overdose, or a fierce autoimmune flare; below five times normal, the cause is usually fatty liver ¹⁴. The old teaching that AST twice ALT means alcohol is half right: that ratio also rises in advanced cirrhosis, so in a non-drinker it flags scarring ⁵.

Read your own panel in this order.

The diseases this catches don't announce themselves. Fatty liver sits quietly for a decade before it inflames and another before it scars ⁸. Chronic hepatitis C is years of shrugged-off ALT bumps, then cirrhosis at sixty that eight weeks of pills at forty would have cured ⁹. Hereditary iron overload and primary biliary cholangitis run the same silent arc ¹⁰. The numbers sat on every yearly draw, unread.