Liver Function Tests

Introduction and Core Markers of Liver Function

Liver function tests, commonly called LFTs, are blood panels that assess the health and metabolic efficiency of the liver. These assays measure specific serum enzymes, proteins, and waste products to detect inflammation, cellular injury, or obstructed bile flow. While termed liver function tests, many components actually evaluate liver integrity and biliary excretion rather than direct metabolic capacity. Clinicians use these panels alongside patient history and physical examinations to diagnose acute hepatitis, chronic cirrhosis, and drug-induced liver injuries in Nigerian healthcare settings.

Enzymes Indicating Hepatocellular Injury

When liver cells sustain damage, intracellular enzymes leak into the bloodstream, elevating serum levels.

• Alanine Aminotransferase (ALT): An enzyme found primarily in the liver, making it the most specific marker for hepatocellular injury.
• Aspartate Aminotransferase (AST): Present in the liver, cardiac muscle, skeletal muscle, and kidneys, rendering it less specific to the liver than ALT.
• AST to ALT Ratio: An elevated ratio exceeding 2:1 strongly suggests alcoholic liver disease, whereas viral hepatitis typically presents with higher ALT than AST.

Markers of Biliary Tract Integrity and Obstruction

Bile flow disruption or biliary tract irritation causes a distinct elevation in specific serum enzymes located along the canalicular membrane and bile duct epithelium.

• Alkaline Phosphatase (ALP): Found in the liver, bones, placenta, and intestines. Elevation points to biliary obstruction or bone pathology.
• Gamma-Glutamyl Transferase (GGT): An enzyme highly sensitive to biliary disease and alcohol ingestion. Used to confirm that an elevated ALP originates from the liver rather than bone.
• Bilirubin (Conjugated and Unconjugated): Measures the liver's ability to process and excrete heme breakdown products. Elevated conjugated bilirubin indicates post-hepatic or hepatocellular cholestasis.

Markers of Hepatic Synthesis and Synthetic Function

The liver synthesizes vital plasma proteins. Measuring these proteins assesses the liver's ongoing functional capacity rather than just cellular injury.

• Serum Albumin: The main protein produced by the liver. Low levels reflect chronic liver dysfunction, as albumin has a long half-life of about twenty days.
• Prothrombin Time (PT) and INR: Measures the clotting factors synthesized by the liver. Because these factors have short half-lives, an abnormal PT or INR is a sensitive indicator of both acute and chronic hepatic failure.

Clinical Indications for Ordering LFTs

Clinicians order liver function tests for various diagnostic, monitoring, and screening purposes. Common indications include investigating signs of jaundice, right upper quadrant abdominal pain, unexplained fatigue, or hepatomegaly. LFTs are also essential for monitoring patients taking hepatotoxic medications such as antituberculosis drugs used extensively in Nigeria. Furthermore, these panels help stage chronic conditions like hepatitis B and C, monitor response to antiviral therapies, and evaluate systemic illnesses that affect secondary organs.

Nursing Responsibilities and Patient Preparation

Nurses play a vital role in preparing patients for diagnostic blood draws and ensuring specimen integrity. While many LFTs require no special preparation, advising the patient about the procedure reduces anxiety. The nurse must verify patient identity, use proper venipuncture technique, and prevent hemolysis during blood collection, as broken red blood cells falsely elevate AST and potassium levels. Post-procedure, the nurse applies pressure to the venipuncture site, monitors for hematoma formation, and ensures prompt transport of the specimen to the laboratory.