Liver Function Tests (LFTs) are a group of blood tests that provide crucial insights into the health and function of the liver. The liver is a vital organ responsible for numerous critical processes, including metabolism, detoxification, protein synthesis, and bile production. LFTs help diagnose, monitor, and manage liver-related conditions by assessing the levels of enzymes, proteins, and other substances produced or processed by the liver.
Clinical Presentations Indicating Liver Function Tests
LFTs are typically recommended by doctors when patients present with signs and symptoms suggestive of liver dysfunction. The liver's extensive role in the body's metabolism and detoxification means that its impairment can manifest in a variety of clinical presentations:
1. Jaundice: Jaundice is characterized by the yellowing of the skin and eyes due to elevated bilirubin levels. It is often the first sign of liver disease and may result from conditions such as hepatitis, cirrhosis, biliary obstruction, or hemolysis.
2. Right Upper Quadrant Abdominal Pain: Pain in the upper right side of the abdomen may indicate liver or gallbladder issues, such as hepatitis, liver abscess, gallstones, or cholecystitis.
3. Fatigue and Weakness: Chronic liver conditions, such as hepatitis B or C, cirrhosis, or liver cancer, may often present with fatigue
4. Nausea and Vomiting: Persistent nausea and vomiting, especially when associated with other symptoms of liver disease, can indicate acute hepatitis, drug-induced liver injury, or cirrhosis.
5. Dark Urine and Pale Stools: These symptoms are indicative of altered bilirubin metabolism and impaired bile flow, commonly seen in cholestasis, biliary atresia, or gallstones.
6. Pruritus (Itching): Severe itching without a clear dermatological cause can occur in liver diseases with cholestasis, such as primary biliary cholangitis or primary sclerosing cholangitis, due to the accumulation of bile acids in the blood.
7. Bleeding Tendencies: Easy bruising, bleeding gums, and prolonged bleeding times suggest impaired liver synthesis of clotting factors, which is common in advanced cirrhosis or liver failure.
8. Ascites and Edema: Fluid accumulation in the abdomen (ascites) and swelling in the legs (edema) are often due to portal hypertension and low serum albumin seen in liver cirrhosis.
9. Hepatic Encephalopathy: Altered mental status, confusion, and even coma can occur in advanced liver disease due to the accumulation of neurotoxins, such as ammonia, which the liver normally detoxifies.
10. Routine Monitoring of Liver Conditions: LFTs are routinely done for patients with known liver conditions like chronic hepatitis B or C, alcoholic liver disease, and non-alcoholic fatty liver disease to monitor disease progression and response to treatment.
11. Drug Monitoring: Some medications can cause liver injury (e.g., acetaminophen, statins, and antiepileptics). LFTs are often performed before starting these drugs and periodically during treatment to monitor liver function.
Supportive Tests in Liver Function Evaluation
LFTs are often supplemented with additional tests depending on the clinical context:
- Imaging Studies (Ultrasound, CT, MRI): These are used to visualize the liver structure, detect tumors, cysts, abscesses, and assess the biliary tree.
- Viral Hepatitis Panel: To identify viral causes of hepatitis, such as hepatitis A, B, C, D, and E.
- Autoimmune Liver Disease Panel: This includes testing for autoimmune hepatitis, primary biliary cholangitis, and primary sclerosing cholangitis.
- Alpha-Fetoprotein (AFP): This is a tumor marker often elevated in hepatocellular carcinoma.
- Serum Ammonia : Elevated levels suggest hepatic encephalopathy.
- Liver Biopsy: Provides histological examination to assess the extent of liver damage.
Preparation of Patients for Liver Function Tests
Proper preparation is essential for accurate LFT results:
1. Fasting: Fasting for 8-12 hours before the test is recommended, although not always necessary for basic liver enzyme measurements. Fasting helps minimize interference from recent food intake, especially for lipid profile components.
2. Avoid Alcohol : Patients should avoid alcohol consumption for at least 24-48 hours before testing, as alcohol can transiently elevate liver enzymes, particularly gamma-glutamyl transferase (GGT).
3. Medication Review : A detailed review of medications, including over-the-counter drugs and herbal supplements, is crucial as many can affect liver enzymes (e.g., acetaminophen, antibiotics, and statins).
4. Adequate Hydration: Patients should maintain good hydration; however, dehydration does not significantly affect liver enzymes but may influence other test parameters.
5. Avoid Heavy Meals: Large or fatty meals should be avoided before the test to prevent temporary elevations in liver enzymes.
Laboratory Procedure for Liver Function Tests
1. Materials Required:
- Sterile needles and syringes for venipuncture.
- Tourniquet to facilitate vein access.
- Alcohol swabs to disinfect the blood draw site.
- Blood collection tubes, typically with serum separators (yellow or red tops).
- Labels and requisition forms for proper sample identification.
2. Procedure:
- Patient Positioning: The patient is seated comfortably with the arm extended.
- Venipuncture Site Preparation: The antecubital fossa (inner elbow) is commonly used. The site is cleaned with an alcohol swab in a circular motion.
- Blood Collection: A tourniquet is applied above the site, and blood is drawn into the collection tubes. The tourniquet is released before withdrawing the needle to prevent hematoma formation.
- Handling of Specimens: Blood samples are labeled and gently inverted to mix. They are promptly transported to the laboratory for processing.
3. Laboratory Analysis:
- The serum is analyzed using automated analyzers that perform enzyme assays, colorimetric assays, and immunoassays.
- Results are generated in numerical values and compared to established reference ranges.
Parameters Tested in LFT and Their Detailed Significance
1. Alanine Aminotransferase (ALT)
(SGPT (Serum Glutamate Pyruvate Transaminase))
- Function: ALT is predominantly found in the liver and plays a role in amino acid metabolism. It is released into the blood when liver cells are damaged.
- Clinical Significance: Elevated ALT levels are highly specific to liver cell injury, such as in viral hepatitis, fatty liver disease, and toxic liver injury.
- Normal Values: 7-56 U/L.
2. Aspartate Aminotransferase (AST)
(SGOT (Serum Glutamate Oxaloacetate Transaminase))
- Function: AST is present in the liver, heart, muscle, and other tissues, playing a role in amino acid metabolism.
- Clinical Significance: Elevated AST suggests liver damage but is less specific than ALT due to its presence in other tissues. An AST/ALT ratio >2 is often seen in alcoholic liver disease.
- Normal Values: 10-40 U/L.
3. Alkaline Phosphatase (ALP)
- Function: ALP is found in the liver, bones, bile ducts, and placenta. It helps break down proteins and is linked to bile flow.
- Clinical Significance: Elevated ALP indicates cholestasis, bile duct obstruction, liver tumors, or bone disease.
- Normal Values: 40-129 U/L.
4. Gamma-Glutamyl Transferase (GGT)
- Function: GGT is involved in glutathione metabolism and is sensitive to liver and bile duct issues.
- Clinical Significance: Elevated GGT indicates liver damage, bile duct issues, and alcohol consumption.
- Normal Values: 9-48 U/L.
5. Bilirubin (Total and Direct)
- Function: Bilirubin is a breakdown product of red blood cells processed by the liver. Total bilirubin includes unconjugated (indirect) and conjugated (direct) forms.
- Clinical Significance: High bilirubin levels cause jaundice and indicate liver dysfunction, hemolysis, or biliary obstruction. Direct bilirubin elevation suggests hepatic or post-hepatic causes.
- Normal Values: Total: 0.1-1.2 mg/dL; Direct: 0.0-0.3 mg/dL.
6. Albumin
- Function: Albumin is the main protein made by the liver, maintaining oncotic pressure and transporting hormones, vitamins, and drugs.
- Clinical Significance: Low albumin levels suggest chronic liver disease, cirrhosis, malnutrition, or protein-losing enteropathy.
- Normal Values: 3.5-5.0 g/dL.
7. Total Protein
- Function: Measures the total amount of albumin and globulins in the blood.
- Clinical Significance: Abnormal levels may indicate liver or kidney disease, malnutrition, or chronic inflammation.
- Normal Values: 6.0-8.3 g/dL.
8. Prothrombin Time (PT) and International Normalized Ratio (INR)
- Function: PT measures how long it takes blood to clot, assessing the liver’s ability to produce clotting factors. INR standardizes PT results for global comparison.
- Clinical Significance: Prolonged PT/INR indicates impaired liver synthesis of clotting factors, common in severe liver disease, vitamin K deficiency, or anticoagulant use.
- Normal Values: PT: 11-13.5 seconds; INR: 0.8-1.1.
Connection between these Parameters with Liver Function:
1. ALT and AST: These enzymes are released when liver cells are damaged. ALT is more liver-specific, whereas AST is found in multiple tissues. Their elevation reflects hepatocellular injury, seen in conditions like viral hepatitis, alcoholic liver disease, and non-alcoholic fatty liver disease.
2. ALP and GGT: Both enzymes are associated with bile flow. ALP is elevated in bile duct obstruction, cholestasis, or liver tumors. GGT is often elevated with ALP in liver and biliary diseases, and it is particularly sensitive to alcohol use.
3. Bilirubin: Bilirubin metabolism is a key function of the liver, and its measurement helps assess the liver's capacity to process and excrete this waste product. Elevated bilirubin levels point to liver dysfunction, hemolysis, or bile duct blockages.
4. Albumin and Total Protein: The liver synthesizes albumin, and its levels provide insight into the liver’s synthetic function. Low levels may indicate chronic liver disease, malnutrition, or protein loss through the kidneys or gastrointestinal tract.
5. PT/INR: These tests assess the liver’s ability to produce clotting factors, which are essential for normal blood coagulation. Prolonged PT/INR suggests advanced liver dysfunction, vitamin K deficiency, or the presence of anticoagulants.
Conclusion
Liver Function Tests are invaluable in diagnosing, monitoring, and managing liver diseases. By evaluating enzymes, proteins, and other substances produced by the liver, LFTs provide a comprehensive picture of liver health. Understanding the significance of each parameter helps clinicians interpret results accurately, leading to timely and appropriate management of liver-related conditions.
(Notes collected by Dr Jayaram Krishna M)
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