Liver Function Test (LFT)

 

Liver Function Test (LFT)



Introduction

A Liver Function Test (LFT) is 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 bilirubin in the blood. LFTs help diagnose liver diseases, monitor the progression of liver disorders, assess the severity of liver damage, and evaluate the effectiveness of treatment.

The liver is one of the largest and most important organs in the human body. It performs numerous vital functions, including metabolism of carbohydrates, proteins, and fats; detoxification of harmful substances; production of bile; storage of vitamins and minerals; and synthesis of plasma proteins such as albumin and clotting factors. Any damage to liver cells can alter the levels of these substances in the blood, making LFTs valuable indicators of liver health.

Definition

Liver Function Test (LFT) is a panel of blood tests that measures liver enzymes, proteins, bilirubin, and other biochemical markers to evaluate liver function, detect liver disease, monitor disease progression, and assess treatment response.

Objectives of LFT

The major objectives of Liver Function Tests are:

  • To assess liver function.
  • To detect liver diseases at an early stage.
  • To diagnose hepatitis and jaundice.
  • To evaluate liver injury caused by alcohol, drugs, or toxins.
  • To monitor chronic liver diseases such as cirrhosis.
  • To assess bile duct obstruction.
  • To monitor the effectiveness of treatment.
  • To evaluate liver function before surgery.
  • To investigate unexplained abdominal pain or jaundice.
  • To assess patients with suspected fatty liver disease.

Principle of the Test

LFT is based on the measurement of specific enzymes, proteins, and pigments present in the blood. Damage to liver cells releases intracellular enzymes into the bloodstream, while impaired liver function affects the production of proteins and the metabolism of bilirubin. These changes are measured using automated biochemical analyzers.

Sample Required

  • Specimen: Venous blood
  • Sample type: Serum (preferred)
  • Collection tube: Plain red-top tube or Serum Separator Tube (SST)
  • Sample volume: 3–5 mL of blood

Patient Preparation

  • Fasting is generally not required, although some laboratories may recommend 8–12 hours of fasting.
  • Avoid alcohol for at least 24 hours before the test.
  • Inform the healthcare provider about any medications or herbal supplements.
  • Avoid strenuous exercise before sample collection if advised.

Procedure

  1. Verify the patient's identity.
  2. Clean the venipuncture site with an antiseptic.
  3. Collect 3–5 mL of venous blood.
  4. Transfer blood into a plain or SST tube.
  5. Allow the blood to clot.
  6. Centrifuge to separate the serum.
  7. Analyze the serum using an automated biochemistry analyzer.

Components of Liver Function Test (LFT)

1. Alanine Aminotransferase (ALT/SGPT)

Function

ALT is an enzyme found mainly in liver cells. It is released into the bloodstream when liver cells are damaged.

Normal Range

7–56 U/L

Increased in

  • Acute viral hepatitis
  • Chronic hepatitis
  • Fatty liver disease
  • Liver cirrhosis
  • Drug-induced liver injury
  • Liver tumors

Clinical Significance

ALT is considered one of the most specific indicators of liver cell injury.

2. Aspartate Aminotransferase (AST/SGOT)

Function

AST is present in the liver, heart, skeletal muscles, kidneys, and brain.

Normal Range

10–40 U/L

Increased in

  • Liver disease
  • Alcoholic hepatitis
  • Myocardial infarction
  • Muscle injury
  • Cirrhosis

Clinical Significance

AST is less specific than ALT because it is also present in other tissues.

3. Alkaline Phosphatase (ALP)

Function

ALP is mainly found in the liver, bile ducts, and bones.

Normal Range

44–147 U/L

Increased in

  • Bile duct obstruction
  • Cholestasis
  • Liver tumors
  • Bone diseases
  • Pregnancy

Clinical Significance

Elevated ALP often indicates obstruction of bile flow.

4. Gamma-Glutamyl Transferase (GGT)

Function

GGT is an enzyme present in liver cells and bile ducts.

Normal Range

9–48 U/L

Increased in

  • Alcoholic liver disease
  • Cholestasis
  • Liver tumors
  • Drug-induced liver injury

Clinical Significance

GGT helps confirm that elevated ALP originates from the liver rather than bone.

5. Total Bilirubin

Function

Bilirubin is produced during the breakdown of red blood cells and is processed by the liver.

Normal Range

0.3–1.2 mg/dL

Increased in

  • Jaundice
  • Hepatitis
  • Cirrhosis
  • Hemolytic anemia
  • Bile duct obstruction

Clinical Significance

Elevated bilirubin causes yellow discoloration of the skin and eyes (jaundice).

6. Direct (Conjugated) Bilirubin

Normal Range

0.0–0.3 mg/dL

Increased in

  • Obstructive jaundice
  • Hepatitis
  • Cholestatic liver disease

7. Indirect (Unconjugated) Bilirubin

Normal Range

0.2–0.9 mg/dL

Increased in

  • Hemolytic anemia
  • Gilbert syndrome
  • Neonatal jaundice

8. Albumin

Function

Albumin is the major protein synthesized by the liver.

Normal Range

3.5–5.0 g/dL

Decreased in

  • Chronic liver disease
  • Cirrhosis
  • Malnutrition
  • Kidney disease
  • Protein-losing disorders

Clinical Significance

Low albumin indicates impaired liver synthetic function or protein loss.

9. Total Protein

Normal Range

6.0–8.3 g/dL

Increased in

  • Chronic inflammation
  • Multiple myeloma

Decreased in

  • Liver disease
  • Malnutrition
  • Kidney disease

10. Globulin

Normal Range

2.0–3.5 g/dL

Increased in

  • Chronic liver disease
  • Autoimmune disorders
  • Chronic infections

11. Albumin/Globulin (A/G) Ratio

Normal Range

1.0–2.5

Decreased in

  • Cirrhosis
  • Chronic liver disease
  • Autoimmune disorders

12. Prothrombin Time (PT) / International Normalized Ratio (INR)

Function

Measures the liver's ability to produce clotting factors.

Normal Values

  • PT: 11–13.5 seconds
  • INR: 0.8–1.2

Prolonged in

  • Severe liver disease
  • Vitamin K deficiency
  • Liver failure

Clinical Significance

A prolonged PT/INR suggests reduced liver synthetic function and an increased risk of bleeding.

Interpretation of LFT Results

Finding

Possible Condition

High ALT and AST

Hepatitis, liver cell injury

AST > ALT

Alcoholic liver disease

High ALP and GGT

Bile duct obstruction, cholestasis

High Bilirubin

Jaundice, hepatitis, hemolysis

Low Albumin

Cirrhosis, chronic liver disease

Prolonged PT/INR

Liver failure, impaired clotting factor synthesis

Diseases Diagnosed by LFT

  • Viral hepatitis (A, B, C, etc.)
  • Alcoholic liver disease
  • Non-alcoholic fatty liver disease (NAFLD)
  • Liver cirrhosis
  • Liver cancer
  • Cholestasis
  • Bile duct obstruction
  • Drug-induced liver injury
  • Autoimmune hepatitis
  • Hemochromatosis
  • Wilson disease

Advantages

  • Simple blood test
  • Minimally invasive
  • Early detection of liver disease
  • Helps diagnose different liver disorders
  • Monitors disease progression
  • Assesses treatment response
  • Widely available and cost-effective

Limitations

  • Abnormal results do not always indicate liver disease.
  • Some liver diseases may have normal LFT results, especially in early stages.
  • Enzyme levels can be influenced by medications, alcohol, muscle injury, or pregnancy.
  • Additional investigations (ultrasound, CT scan, MRI, viral markers, or liver biopsy) may be required for a definitive diagnosis.

Precautions

  • Avoid alcohol before testing.
  • Inform the healthcare provider about all medications and supplements.
  • Follow laboratory instructions regarding fasting if requested.
  • Ensure proper blood sample handling to prevent hemolysis.

Clinical Significance

Liver Function Tests are among the most commonly requested laboratory investigations in clinical practice. They help clinicians evaluate liver health, distinguish between hepatocellular injury and cholestatic disease, monitor chronic liver conditions, and guide treatment decisions. When interpreted together with the patient's history, physical examination, and imaging studies, LFTs provide essential information for diagnosing and managing liver disorders.

Conclusion

The Liver Function Test (LFT) is a comprehensive panel of blood tests used to assess liver function and detect liver disease. It measures liver enzymes (ALT, AST, ALP, GGT), bilirubin, proteins (albumin and total protein), and clotting function (PT/INR). LFTs are essential for diagnosing liver disorders, monitoring disease progression, evaluating treatment effectiveness, and assessing the liver's synthetic and excretory functions. Their simplicity, reliability, and clinical value make them an indispensable part of routine medical practice.

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