Liver Function Tests

Definition of Liver Function Tests

  • Liver Function Tests (LFTs): Blood parameters that indicate liver functionality and potential liver injury.

    • Purpose: Assess liver health by measuring levels of certain enzymes and proteins in the blood.

Key Components of Liver Function Tests

  • Enzymes: Indicators of liver injury. High levels suggest liver disease.

    • Aspartate Transaminase (AST)

    • Alanine Transaminase (ALT)

    • Alkaline Phosphatase (ALP)

    • Gamma-Glutamyl Transferase (GGT)

  • Liver Products: Assess liver function and synthesis capabilities.

    • Albumin: Protein produced by the liver; low levels indicate liver dysfunction.

    • Prothrombin Time (PT): Measures clotting factors; prolonged PT suggests liver impairment.

    • Bilirubin: Processed in the liver; elevated levels indicate issues with bilirubin conjugation/excretion.

Reasons for Ordering Liver Function Tests

  • Patient History: Concern for liver disease in patients with related history.

    • History of liver disease

    • Symptoms like jaundice (yellow discoloration)

  • Potential Liver Injury: Investigating causes of liver dysfunction.

    • Medication exposure (e.g., hepatotoxic drugs like paracetamol/acetaminophen)

    • Alcohol history

    • Family history of liver disease (e.g., hemochromatosis)

  • High-Risk Groups: Screening for individuals with specific risk factors.

    • History of blood transfusion

    • Exposure to viral hepatitis

    • Illicit drug use

  • Extrahepatic Causes: Conditions outside the liver may impact liver function.

    • Malignancy (e.g., secondary liver cancer)

    • Hypoxia (low oxygen/blood flow, e.g., history of shock)

    • Monitoring effects of medications (e.g., methotrexate, valproate)

Analysing Liver Function Tests in Patients with Jaundice

  • Jaundice: Yellow discoloration of skin/eyes due to bilirubin accumulation.

    • Critical parameter: Bilirubin level > 1.2 mg/dL

Bilirubin Metabolism

  • Source of Bilirubin: Breakdown product of red blood cells (average lifespan: 120 days).

    • Components recycled:

      • Iron returned to the liver

      • Protein globulins converted to amino acids

    • Heme component -> converted to bilirubin by macrophages.

  • Types of Bilirubin:

    • Unconjugated Bilirubin: Bound to albumin, transported to the liver for conjugation.

    • Conjugated Bilirubin: Water-soluble form excreted into bile.

Liver Lobule Structure and Function

  • Liver Lobules: Hexagonal units with central vein (site of blood accumulation).

    • Central vein in the centre which is the accumulation of blood that has diffused or percolated through all the hepatocytes and then all of the central vein blood will eventually accumulate and then leave the liver via the inferior Vena cava.

    • Blood Supply: 20% arterial + 70-80% portal vein. These bloods merge together as the sinusoid and go through these plates of cells called the parasite and what goes on the opposite direction is bile caliculi. Which is like a river of bile that goes out towards the outer part of the lobule and these bile ducts will come together from the hepatic ducts then become

    • Bile Canaliculi: Transport bile out from lobules.

Role of Hepatocytes

  • Hepatocytes: Liver cells that process blood and produce bile.

    • Convert unconjugated bilirubin to conjugated bilirubin through UGT enzyme.

    • Bile is excreted, contributing to digestion and elimination of bilirubin.

Causes of Elevated Bilirubin in Jaundice

  • Pre-Hepatic Causes: Increased red blood cell destruction.

    • Conditions:

      • Hemolytic anemia

      • Hemorrhage or hematoma

  • Understanding Bilirubin Elevation: Evaluation of liver function tests helps identify the underlying cause of jaundice.