LIVER FUNCTION TEST (LFT)

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LIVER FUNCTION TEST (LFT)

1. What is Liver Function Test (LFT)?

Liver Function Tests (LFTs) are a group of blood tests used to evaluate the health and functioning of the liver. These tests measure the levels of liver enzymes, proteins, and waste products in the blood. They help diagnose liver diseases, detect liver damage, monitor disease progression, and assess the effectiveness of treatment. LFTs also identify problems related to bile ducts and the liver’s ability to produce proteins and clotting factors. Doctors commonly recommend LFTs when symptoms such as jaundice, abdominal pain, fatigue, or abnormal liver function are suspected. LFTs play an important role in early diagnosis and disease management.

2. When is LFT Recommended?

Liver Function Tests are recommended whenever liver disease or liver damage is suspected. Doctors advise LFTs for patients with symptoms such as jaundice, fatigue, abdominal pain, nausea, dark urine, or pale stools. They are commonly performed to diagnose hepatitis, fatty liver disease, alcohol-related liver damage, and drug-induced liver injury. LFTs are also useful before starting medications that may affect the liver and during routine health check-ups. Individuals with obesity, diabetes, excessive alcohol consumption, or a family history of liver disease may also require regular LFT monitoring to detect liver problems at an early stage.

3. ALT (Alanine Aminotransferase)

Alanine Aminotransferase (ALT) is an enzyme found mainly in liver cells. Normally, only small amounts of ALT are present in the bloodstream. When liver cells are damaged due to infections, inflammation, toxins, or injury, ALT leaks into the blood, causing its level to rise. Therefore, ALT is considered one of the most liver-specific enzymes. Elevated ALT levels are commonly seen in hepatitis, fatty liver disease, liver cirrhosis, and drug-induced liver injury. Monitoring ALT helps doctors assess the severity of liver damage and evaluate the response to treatment. The normal range is approximately 7–56 U/L.

4. AST (Aspartate Aminotransferase)

Aspartate Aminotransferase (AST) is an enzyme present in the liver, heart, skeletal muscles, kidneys, and brain. Unlike ALT, AST is not specific to the liver. Increased AST levels may indicate liver diseases such as hepatitis or cirrhosis, but they can also result from muscle injury, heart attack, or strenuous exercise. Therefore, AST is usually interpreted together with ALT to determine the cause of elevated enzyme levels. A higher ALT compared to AST generally suggests liver disease. The normal AST level ranges from 10–40 U/L, depending on the laboratory reference values.

5. ALP (Alkaline Phosphatase)

Alkaline Phosphatase (ALP) is an enzyme found mainly in the liver, bile ducts, bones, intestines, and placenta. High ALP levels often indicate bile duct obstruction, liver disease, or increased bone activity. Elevated ALP is commonly seen in conditions such as gallstones, bile duct blockage, bone disorders, and healing fractures. Since ALP is present in several tissues, doctors usually measure it along with Gamma-Glutamyl Transferase (GGT) to confirm whether the increase is due to liver disease. The normal range of ALP is approximately 44–147 U/L and varies slightly among laboratories.

6. GGT (Gamma-Glutamyl Transferase)

Gamma-Glutamyl Transferase (GGT) is an enzyme found mainly in the liver and bile ducts. It is highly sensitive to liver injury caused by alcohol, medications, and bile duct diseases. Elevated GGT levels often indicate alcohol-related liver disease, bile duct obstruction, hepatitis, or liver inflammation. GGT is commonly measured together with ALP because an increase in both enzymes strongly suggests a liver or bile duct problem rather than a bone disorder. Although GGT is very sensitive, it is not highly specific because its level can also rise due to certain medications and lifestyle factors. Normal range: 9–48 U/L.

7. Bilirubin (Total)

Bilirubin is a yellow pigment produced during the breakdown of old red blood cells. The liver processes bilirubin and removes it from the body through bile. Elevated bilirubin levels occur when the liver cannot process it properly or when bile flow is blocked. High bilirubin causes jaundice, characterized by yellowing of the skin and eyes. Increased bilirubin may result from hepatitis, liver cirrhosis, bile duct obstruction, gallstones, or excessive destruction of red blood cells. Measuring bilirubin helps diagnose liver disorders, bile duct diseases, and certain blood disorders. The normal range is 0.3–1.2 mg/dL.

8. Albumin

Albumin is the most abundant protein produced by the liver. It helps maintain blood volume, transports hormones, vitamins, drugs, and minerals, and prevents fluid leakage from blood vessels. Low albumin levels indicate reduced liver protein synthesis and may suggest chronic liver disease, cirrhosis, malnutrition, kidney disease, or severe infections. Albumin levels are useful for assessing long-term liver function rather than acute liver injury. Since albumin has a relatively long half-life, it reflects chronic changes in liver health. The normal blood albumin concentration ranges from 3.5–5.0 g/dL, depending on laboratory standards.

9. Total Protein

Total Protein measures the combined concentration of albumin and globulin proteins in the blood. These proteins are essential for immunity, blood clotting, transport of nutrients, and maintenance of fluid balance. Abnormal total protein levels may indicate liver disease, kidney disorders, malnutrition, dehydration, or immune system disorders. Since the liver synthesizes many blood proteins, total protein helps evaluate the liver’s protein-producing ability. It is usually interpreted along with albumin and globulin levels for better diagnosis. The normal total protein level ranges from 6.0–8.3 g/dL, although slight variations exist between laboratories.

10. Prothrombin Time (PT/INR)

Prothrombin Time (PT) and International Normalized Ratio (INR) measure how long blood takes to clot. The liver produces several clotting factors required for normal blood coagulation. When liver function declines, clotting factor production decreases, causing prolonged PT and increased INR values. Therefore, PT/INR is an important indicator of the liver’s synthetic function. It is commonly used to assess the severity of liver disease and monitor patients with liver failure. PT is also useful before surgery to evaluate bleeding risk. The normal PT is 11–13.5 seconds, and the normal INR is 0.8–1.2.

11. Common Liver Diseases Detected by LFT

Liver Function Tests help diagnose several liver disorders. These include viral hepatitis, which causes liver inflammation; fatty liver disease, resulting from excessive fat accumulation in liver cells; cirrhosis, where healthy liver tissue is replaced by scar tissue; liver failure, in which the liver loses its ability to perform essential functions; and bile duct obstruction, which blocks bile flow and increases liver enzymes. LFTs also help monitor alcohol-related liver disease, drug-induced liver injury, and chronic liver disorders. Early detection through LFTs allows timely treatment, preventing complications and improving patient outcomes.

12. Quick Facts about LFT

Liver Function Tests are an important topic for Biology. ALT is more specific for liver damage than AST. Simultaneous elevation of ALP and GGT usually indicates bile duct obstruction or cholestatic liver disease. High bilirubin levels cause jaundice, resulting in yellow discoloration of the skin and eyes. Low albumin suggests chronic liver disease or poor nutritional status. PT/INR is the best indicator of the liver’s ability to produce clotting factors and reflects liver synthetic function. Together, these tests provide a comprehensive assessment of liver health, disease severity, and treatment response.