Liver tests: hepatocellular or cholestatic?

What it is

The so-called liver function tests are mostly markers of injury, not of function. The aminotransferases (ALT and AST) leak from damaged liver cells; ALT is more specific to the liver, while AST is also found in heart, skeletal muscle, kidney and red cells. Alkaline phosphatase (ALP) and gamma-glutamyl transferase (GGT) rise when bile flow is impaired; ALP also comes from bone, the placenta and the intestine, and a raised GGT alongside it confirms a hepatobiliary source. Bilirubin is split into unconjugated (indirect), raised by haemolysis or poor conjugation as in Gilbert syndrome, and conjugated (direct), raised in liver cell disease and cholestasis. The true tests of synthetic function are albumin and the prothrombin time or INR, which can stay normal until disease is advanced. The reading question is which pattern dominates: hepatocellular (aminotransferases out of proportion to ALP), cholestatic (ALP and GGT out of proportion), mixed, or isolated hyperbilirubinaemia. The pattern, the size and speed of the rise and the clinical story then narrow the causes, and an ultrasound separates obstruction of the large ducts from cholestasis inside the liver.

Reference values and concepts

• Usual adult ranges (they vary by laboratory): ALT 7–56 U/L, AST 10–40 U/L, ALP 44–147 U/L.
• Total bilirubin 0.1–1.2 mg/dL; conjugated (direct) bilirubin below 0.3 mg/dL; jaundice is usually visible above about 2.5–3 mg/dL.
• Albumin 3.5–5.0 g/dL; its long half-life (about 3 weeks) means it falls late, and it also falls in malnutrition, nephrotic syndrome and inflammation.
• The prothrombin time and INR rise when the liver cannot make clotting factors; vitamin K deficiency from cholestasis does the same and corrects with vitamin K.
• ALT is more liver-specific than AST; AST also rises with muscle injury, so check creatine kinase when AST leads without another explanation.
• GGT rises with cholestasis, alcohol and enzyme-inducing drugs; a raised ALP with a normal GGT suggests bone, pregnancy or growth in children.

Reading it step by step

1. Confirm the abnormality and compare with old results — a single mild rise in a well patient is often repeated before a full workup.
2. Decide which is more raised for its upper limit, ALT or ALP — this splits hepatocellular from cholestatic causes.
3. Calculate the R ratio when the pattern is unclear — above 5 is hepatocellular, below 2 cholestatic, between them mixed.
4. Grade the size of the rise — mild (under 5 times normal), marked, or in the thousands, each with its own short list of causes.
5. Look at bilirubin and its fractions — unconjugated alone points to haemolysis or Gilbert; conjugated to the liver or bile ducts.
6. Check albumin and INR — they show whether the liver still makes its proteins and how ill the patient is.
7. If ALP leads, confirm a liver source with GGT, then ultrasound — dilated ducts mean obstruction; non-dilated, a cause inside the liver.
8. Match with the history: alcohol, drugs, supplements, travel, viral risk factors, metabolic syndrome, pregnancy — they choose the targeted tests.

Patterns of liver tests and what they suggest

Patterns and common mistakes

• Calling every abnormal result 'liver failure': most rises are injury markers; failure means a high INR, low albumin, jaundice or encephalopathy.
• Missing a source outside the liver: AST from muscle (exercise, rhabdomyolysis), ALP from bone or pregnancy, unconjugated bilirubin from haemolysis.
• Normal aminotransferases do not exclude cirrhosis: a scarred liver may show normal enzymes with low albumin, high INR and low platelets.
• Paracetamol (acetaminophen) poisoning may show normal tests early; the time of ingestion and the drug level decide treatment, not the first ALT.
• Mild isolated unconjugated hyperbilirubinaemia that rises with fasting or illness, with normal enzymes and no haemolysis, is typical of Gilbert syndrome.
• Fever, jaundice and right upper quadrant pain with a cholestatic pattern is cholangitis until proven otherwise.
• Drug-induced injury with ALT above 3 times normal and bilirubin above 2 times normal (Hy's law) carries a high risk of a severe outcome.

Next step

• Signs of acute liver failure (raised INR, confusion) or suspected paracetamol overdose: call a senior now; overdose needs a timed drug level and the antidote acetylcysteine by protocol.
• Cholestatic pattern: request an abdominal ultrasound; dilated ducts lead to imaging of the biliary tree and possibly ERCP, and fever with jaundice is an emergency.
• Hepatocellular pattern: viral serology (hepatitis A IgM, hepatitis B surface antigen and core IgM, hepatitis C antibody), autoantibodies, iron studies, and ceruloplasmin in young patients.
• Stop suspected liver-toxic drugs and supplements, ask about alcohol, and repeat the panel to follow the trend.
• Mild persistent rise: look for metabolic dysfunction-associated fatty liver with an ultrasound, assess fibrosis risk, and refer if it persists.

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Elsewhere in DurgiPedia

• Liver function tests: reading the pattern
• Bilirubin
• Alanine aminotransferase (ALT, GPT)
• Aspartate aminotransferase (AST, GOT)
• Serum albumin as a lab test
• Functions of the liver
• Jaundice: prehepatic, hepatic and posthepatic

Connections

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Educational content; it does not replace supervised hands-on training, your institution's protocols or a prescriber's order. A procedure is learnt with a teacher and done only once you are trained to do it.

Sources: Liver Function Tests (StatPearls (NCBI Bookshelf), 2026).

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