Understand liver markers in your lab result

ALT is an enzyme produced mainly in liver cells. Small amounts normally circulate in the blood, but when liver cells are damaged they release more ALT, raising the blood level.

AST is an enzyme found in the liver, heart muscle, skeletal muscle, and red blood cells. It is released into the bloodstream when these tissues are stressed or injured, which is why it is read alongside ALT, GGT, bilirubin and ALP rather than in isolation.

GGT is a liver enzyme found in the bile ducts and liver cells. It is one of the earliest enzymes to react to bile-flow stress and alcohol exposure, which is why it is usually read alongside ALT, AST, ALP and bilirubin rather than alone.

ALP is an enzyme found mainly in the liver, the bile ducts, and the bones. Because it is shared between two unrelated systems, an ALP value should always be read together with GGT, bilirubin, ALT/AST, calcium and vitamin D — the surrounding pattern is what tells liver from bone.

Bilirubin is the yellow pigment produced when the body recycles old red blood cells. Total bilirubin combines two forms — direct (processed by the liver) and indirect (unprocessed) — and is most informative when read alongside direct bilirubin, ALT, AST, ALP, GGT and any symptoms such as jaundice.

Direct bilirubin is the water-soluble form that the liver has processed and is sending out through the bile ducts. It is most useful when read alongside total bilirubin, ALP, GGT and the liver enzymes ALT and AST — the split tells the clinical story.

Albumin is the most abundant protein in blood, produced by the liver. It carries hormones, vitamins, and drugs through the bloodstream and helps maintain fluid balance.

Total protein measures the combined concentration of all proteins in the blood, primarily albumin and globulins. It reflects both nutritional status and immune function.

LDH is an enzyme present in many tissues — liver, heart, muscle, red blood cells and more. Because so many tissues release it, LDH is non-specific and should never be interpreted on its own; it is read alongside the liver panel, CBC and any markers the clinician is following.

Globulin is a group of blood proteins (alpha, beta, and gamma fractions, including immunoglobulins). It is often reviewed together with albumin, total protein, and the A/G ratio.

The A/G ratio compares albumin with globulin and is usually interpreted together with total protein and other liver- or inflammation-related markers.