Liver function tests (LFTs)  are a group of blood tests that provide insights into the health and function of the liver. The liver is a vital organ responsible for essential bodily functions, including metabolism, detoxification, digestion, protein synthesis, and bile production. LFT tests provide valuable information about the liver's overall function and can help diagnose and monitor liver diseases. 

What is the Liver Function Test?

Liver function tests are blood tests that evaluate the liver's performance by measuring specific enzymes, proteins, and other substances. High or low levels of these tests with the overall clinical symptoms can provide hints of the underlying cause. The most commonly measured parameters in LFT tests include: 

• Alanine transaminase (ALT): The primary function of the ALT enzyme is to convert proteins into energy for the liver cells. When the liver is damaged, the ALT enzyme starts releasing into the bloodstream, and levels increase. This test is also referred to as SGPT.
• Aspartate transaminase (AST): The AST enzyme helps the body break down amino acids. Increased AST levels may indicate liver damage, liver disease or muscle damage. This test is referred to as SGOT.
• Alkaline phosphatase (ALP): Higher ALP enzyme levels in the blood may indicate liver damage or conditions, such as a blocked bile duct, and certain bone conditions, as this enzyme is also present in bones.
• Total bilirubin: Bilirubin is a yellow substance created when red blood cells break down. It moves through the liver and leaves the body in stool. So, when bilirubin goes up, it's a sign that something might be wrong with the liver or other body parts. 
• Lactate dehydrogenase (LDH): Higher LDH levels may indicate liver damage. However, other conditions also may cause higher than-normal levels of LDH.
• Total protein and albumin levels: The liver produces several proteins, including albumin. Lower-than-usual albumin levels and total protein may mean liver damage, disease, and gastrointestinal and kidney-related conditions.

Purpose of Liver Function Test

The primary purpose of an LFT is to check how well your liver works. These tests help diagnose liver diseases, such as hepatitis, cirrhosis, and fatty liver disease. Doctors rely on LFT blood test results to guide treatment decisions, evaluate treatment response, and monitor overall liver health. Additionally, LFTs can help detect and monitor the side effects of certain medications that may affect liver function.

When is a Liver Function Test Needed?

• A doctor may order Liver function tests if there are signs or symptoms of liver ailments. These may include fatigue, jaundice (yellowing of the skin and eyes), dark urine, pale stools, abdominal pain, and unexplained weight loss. 
• LFTs are also commonly performed as part of routine check-ups, especially for individuals at higher risk of liver diseases, such as those with a history of alcohol abuse, viral hepatitis, or obesity. 
• If you have liver disease, your doctor may use liver function tests (LFTs) to track how the disease is progressing or to see if a treatment is effective. 
• Your doctor may also suggest a LFT blood test to monitor the side effects of certain medicines that are known to affect your liver. 

What Happens During the Liver Function Test?

During an LFT, a laboratory technician will draw a small blood sample from a vein in your arm and send it to a laboratory for further analysis. Once the analysis is complete, your doctor will review and discuss the results with you. Depending on the findings, the doctor may recommend additional tests or treatments. 

Uses of LFT Test 

Liver function tests serve multiple purposes in diagnosing and monitoring liver diseases. 

• Elevated levels of ALT and AST may indicate liver damage, such as hepatitis or cirrhosis. 
• ALP levels can help identify bile duct obstruction or liver diseases affecting the bile ducts. 
• Total bilirubin levels are essential in assessing liver function, as high levels may indicate liver dysfunction or blockage. 
• Albumin levels help monitor liver disease progression and evaluate the patient's nutritional status.

Liver Function Test Procedure

• Preparation: To prepare for an LFT, your doctor may advise you to fast for a specific period before the test. Fasting helps obtain accurate results, especially for tests that measure triglyceride levels. It is essential to follow any instructions provided to ensure reliable and meaningful results. 
• Blood draw: On the day of the test procedure, wear loose-fitting clothing to allow easy access to your arm for blood collection. They will clean the area with an antiseptic wipe and insert a needle into the vein to draw blood. 
• Sample collection: The technician will collect the blood samples into a special tube, depending on the specific tests requested by your doctor. In the laboratory, technicians analyse the blood samples to measure levels of various substances.
• Inform your doctor about any ongoing medicines or supplements that may affect the test results.

What Do Liver Function Test Results Mean?

Doctors typically interpret liver function test results by comparing the measured values to established reference ranges. If the test results fall within the LFT normal range, it generally indicates that the liver is functioning correctly. However, abnormal results may indicate an underlying liver condition, such as: 

• Abnormal ALT and AST levels may suggest liver inflammation or damage. 
• Elevated ALP levels may indicate liver disease or bone disorders. High bilirubin levels may suggest liver dysfunction or blockage. 
• Low albumin levels may indicate liver disease or malnutrition. 
• Elevated PT or INR levels may indicate impaired blood clotting function, which can indicate liver damage or dysfunction.

What Abnormal Results Mean

When liver function test results are higher or lower than the LFT normal range, it is crucial to consult a doctor for further evaluation. Abnormal results may indicate various liver ailments, such as viral hepatitis, non-alcoholic fatty liver disease, alcoholic liver disease, or liver cirrhosis. Additional diagnostic tests, such as imaging studies (CT, MRI, or ultrasound) or liver biopsy, may be necessary to determine the underlying reason and severity of the liver disease.

Conclusion

Liver function tests are crucial in assessing liver health and diagnosing liver diseases. These tests provide valuable information about the liver's overall function and help doctors make informed decisions regarding patient care. If you experience any symptoms of liver disease or have risk factors, it is essential to discuss with your doctor whether an LFT is necessary. Remember, early detection and proper medical intervention can significantly improve outcomes for liver diseases.

FAQs

1. What is a normal level of liver function test?

The normal ranges for liver function test parameters may vary slightly between different laboratories. However, generally accepted reference ranges for liver function test parameters are as follows:

• ALT: 7-55 U/L
• AST: 8-48 U/L
• ALP: 45-115 U/L
• Total bilirubin: 0.1-1.2 mg/dL
• Albumin: 3.4-5.4 g/dL

2. What happens if the liver function test (LFT) is positive?

A positive liver function test indicates abnormal results that may suggest liver damage or dysfunction. Further assessment is necessary to determine the exact cause and severity of the liver condition.

3. What happens if the liver function test (LFT) is negative?

A negative liver function test means the results fall within the normal value, indicating that the liver functions correctly.

4. What parameters are measured in the liver function test?

The liver function test measures various parameters, including alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), total bilirubin, and albumin levels.

5. How long does the liver function test take to perform?

The liver function test procedure itself typically takes only a few minutes. However, the results may take a few days to be available, depending on the tests performed and the laboratory's turnaround time.

6. Can LFT detect fatty liver?

Liver function tests alone cannot confirm the presence of fatty liver disease. However, elevated liver enzymes, such as ALT and AST, may indicate liver damage due to fatty liver disease. Additional examinations, such as imaging studies or liver biopsy, may be required for a definitive diagnosis.