Liver Function Panel

ALT and AST are the leakage enzymes. ALT sits mostly inside liver cells, so when those cells are injured it spills into the blood, which is exactly how MedlinePlus describes it: damaged liver cells release ALT. AST leaks the same way but is less specific, since it also lives in muscle and the heart. When this pair climbs out of proportion to the rest, the reading points at the liver cells themselves, the picture clinicians call hepatocellular.

ALP and GGT report a different problem: blocked or sluggish bile flow, the cholestatic picture. They rise when something dams bile up behind it, from a stone in a duct to a drug reaction. The two tend to move together when the cause is in the liver or the bile ducts, and that shared movement is what makes the combination meaningful where either number alone would be ambiguous. When a high alkaline phosphatase needs a source, the panel may be followed by 5'-nucleotidase, an enzyme that climbs with liver disease but stays put with bone.

The two pigments sit on the function side. Total bilirubin is the waste the liver clears from old red cells, and splitting it into a direct (processed) and an indirect (unprocessed) fraction tells you whether a rise comes from blocked flow or from something upstream of the liver entirely. Most real reports resolve into one of a handful of recognizable shapes.

Because the headline enzymes report damage, the liver's defining jobs barely appear here. Its synthetic work shows up in albumin, the main blood protein the liver builds, which a metabolic panel carries, and in the clotting factors read indirectly through prothrombin time and INR. When those numbers drift, the liver's capacity is genuinely failing, a deeper and more worrying reading than a leaked enzyme. The other half is clearance, which bilirubin tracks.

Around that core sit the specialty add-ons, each chasing a specific cause rather than screening broadly: ceruloplasmin for an inherited copper-handling disorder, and ammonia, which clinicians may add when disease is advanced enough that the liver can no longer clear it. When the enzymes are abnormal without an obvious cause, the panel also makes room for alpha-1 antitrypsin, the liver-made lung protector whose deficiency can quietly drive unexplained liver injury. Amylase and lipase ride along on some abdominal panels but report on the pancreas, not the liver. The grid below shows where each one fits.

What the panel does well is point. A pattern that holds across two draws, rather than a single flagged enzyme on one sheet, is the signal worth acting on. Because these enzymes wander week to week, the direction across repeated draws often says more than any one printout. For a number-by-number walkthrough, the guide to reading a liver panel covers the members in order, and the two comparisons that earn the most attention here are ALT against AST for the hepatocellular read and ALP against GGT for telling liver flow from bone.