Liver function tests (LFTs) are a group of blood tests used to assess the function and integrity of the liver. Abnormal LFTs can suggest liver damage or disease. LFT patterns are often categorized into “hepatitic” (also referred to as “hepatocellular”) and “obstructive” (also referred to as “cholestatic”).
1. Hepatitic (Hepatocellular) Pattern:
- Findings:
- Elevated alanine aminotransferase (ALT) and aspartate aminotransferase (AST), often with ALT > AST.
- AST > ALT is seen in severe disease, ie cirrhosis
- Mildly elevated alkaline phosphatase (ALP).
- Elevated bilirubin levels, particularly in more severe cases.
- Prothrombin time (PT) might be prolonged in severe cases due to decreased production of clotting factors.
- Elevated alanine aminotransferase (ALT) and aspartate aminotransferase (AST), often with ALT > AST.
- Causes:
- Viral Hepatitis: Hepatitis A, B, C, D, E.
- Alcoholic Hepatitis: Due to excessive alcohol consumption.
- Non-alcoholic Fatty Liver Disease (NAFLD) & Non-alcoholic Steatohepatitis (NASH).
- Drug-Induced Liver Injury: Numerous drugs can cause hepatocellular injury.
- Autoimmune Hepatitis: Immune-mediated attack on the liver.
- Ischemic Hepatitis (Shock Liver): Reduced blood flow to the liver due to conditions like heart failure, septic shock, or dehydration.
- Toxic Hepatitis: Exposure to toxins like Amanita mushroom poisoning.
- Other causes: Hemochromatosis, Wilson’s disease, acute Budd-Chiari syndrome, and others.
2. Obstructive (Cholestatic) Pattern:
- Findings:
- Elevated ALP and gamma-glutamyl transferase (GGT).
- Elevated bilirubin, predominantly direct (conjugated) bilirubin.
- Mild elevation in AST and ALT.
- Causes:
- Gallstones (Cholelithiasis): Blocking the bile ducts, leading to cholestasis.
- Primary Biliary Cirrhosis (PBC): An autoimmune disease that affects bile ducts.
- Primary Sclerosing Cholangitis (PSC): Inflammation and scarring of the bile ducts.
- Biliary Stricture: Narrowing of the bile duct, which can be due to surgery, trauma, or inflammation.
- Bile Duct Tumors: Can obstruct the flow of bile.
- Liver Tumors: Especially those impinging on bile ducts.
- Pancreatic Tumors or Pancreatitis: Can obstruct the common bile duct.
- Drugs: Some drugs can cause cholestatic injury, including certain antibiotics, anabolic steroids, and others.
- Infections: Some infections can lead to cholangitis or obstructive patterns.
- Pregnancy: Rarely, intrahepatic cholestasis of pregnancy.
- Other causes: Genetic conditions like Alagille syndrome, cystic fibrosis, and others.
It’s essential to interpret LFTs in the context of the clinical picture, patient history, physical examination, and other tests. For example, an isolated elevation in AST and ALT in a patient with a history of chronic alcohol consumption might suggest alcoholic hepatitis, while the same findings in a patient taking a new medication might raise suspicions for drug-induced liver injury.
Note: In haemolysis or Gilberts the unconjugated bilirubin is elevated.