Liver Function Tests (LFTs) are a group of biochemical investigations used to evaluate the health and functionality of the liver. The liver performs essential functions such as detoxification, metabolism of nutrients and drugs, protein synthesis, bile formation, and storage of vitamins. LFTs help diagnose liver diseases, monitor the progression of hepatic disorders, and assess the impact of medications on liver function. Understanding these tests is essential for healthcare professionals and clinical pharmacists involved in patient care.
Importance of Liver Function Tests
- Diagnose liver diseases such as hepatitis, cirrhosis, and fatty liver.
- Monitor drug-induced liver injury.
- Evaluate jaundice and bilirubin metabolism disorders.
- Assess liver damage and disease progression.
- Guide therapeutic decisions and monitor treatment response.
Bilirubin Levels
Bilirubin is a yellow pigment formed during the breakdown of hemoglobin. LFTs measure total, direct, and indirect bilirubin levels.
1. Total Bilirubin
Elevated total bilirubin suggests liver dysfunction or increased hemolysis.
2. Direct (Conjugated) Bilirubin
Increased levels indicate obstructive jaundice, cholestasis, or hepatocellular disease.
3. Indirect (Unconjugated) Bilirubin
Elevated in hemolytic anemia, Gilbert syndrome, or conditions impairing bilirubin conjugation.
Liver Enzymes
Enzymes released into the bloodstream due to liver cell injury or cholestasis are important diagnostic markers.
1. Alanine Aminotransferase (ALT)
ALT is a specific marker for hepatocellular damage. Elevated ALT indicates acute or chronic hepatitis, drug-induced liver injury, or liver inflammation.
2. Aspartate Aminotransferase (AST)
AST is present in liver, heart, and muscle. Elevated AST suggests liver disease but must be interpreted with ALT.
AST/ALT Ratio
- AST/ALT > 2: Suggestive of alcoholic liver disease.
- ALT > AST: Typical of viral hepatitis.
3. Alkaline Phosphatase (ALP)
ALP is elevated in cholestatic liver disease, biliary obstruction, and bone disorders. High ALP with elevated GGT suggests liver involvement.
4. Gamma-Glutamyl Transferase (GGT)
GGT helps differentiate between hepatic and bone disease. Elevated GGT indicates biliary obstruction or enzyme induction by alcohol and drugs.
Serum Proteins
The liver synthesizes major plasma proteins. Protein levels reflect liver synthetic function.
1. Serum Albumin
Low albumin levels indicate chronic liver disease, malnutrition, or nephrotic syndrome.
2. Globulins
Globulins may be elevated in chronic liver disease, inflammatory conditions, or autoimmune hepatitis.
Coagulation Parameters
The liver produces clotting factors. Coagulation tests help assess functional capacity of the liver.
1. Prothrombin Time (PT)
Prolonged PT suggests impaired liver function or vitamin K deficiency. It is an important prognostic marker in liver failure.
2. International Normalized Ratio (INR)
INR standardizes PT values. Elevated INR indicates decreased synthetic activity of the liver.
Serum Ammonia
Elevated ammonia levels indicate impaired detoxification due to severe liver disease or hepatic encephalopathy.
Liver Function Test Patterns
1. Hepatocellular Pattern
- Markedly elevated ALT and AST
- Mild elevation in ALP
- May indicate viral hepatitis or toxic injury
2. Cholestatic Pattern
- Elevated ALP and GGT
- Moderate increase in bilirubin
- Suggestive of gallstones or biliary obstruction
3. Mixed Pattern
- Moderate elevations in both enzymes and bile markers
- Seen in drug-induced liver injury
Clinical Interpretation of LFTs
Interpreting LFTs requires a combination of enzyme levels, clinical symptoms, imaging, and patient history.
Common Conditions Identified
- Acute viral hepatitis: Very high ALT/AST.
- Alcoholic liver disease: AST/ALT ratio > 2.
- Obstructive jaundice: High ALP and GGT.
- Fatty liver disease: Mild enzyme elevations.
- Cirrhosis: Low albumin, prolonged PT/INR.
Drug-Induced Liver Injury (DILI)
Many medications can cause hepatotoxicity, making LFT monitoring essential in certain therapies.
- Acetaminophen: Dose-dependent hepatotoxicity.
- Anti-tuberculosis drugs (INH, Rifampicin): Liver enzyme elevation.
- Antiepileptics: Valproate and phenytoin may cause liver injury.
- Statins: Mild ALT elevation.
When Are LFTs Ordered?
- Symptoms of jaundice, abdominal pain, fatigue.
- Chronic alcohol use.
- Monitoring hepatotoxic medications.
- Suspected viral hepatitis.
- Unexplained weight loss or systemic illness.
Detailed Notes:
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