Liver Function Tests (LFT): Types, Normal Functions, Indications and Importance

The liver is the largest gland in the human body. It is located in the abdominal cavity behind the diaphragm. It is dark red or brownish in colour and weighs around 1200 to 1600 grams. Understanding liver function tests is crucial for diagnosing liver diseases and jaundice.

Normal Functions of the Liver:

1. Manufacture and elimination of Bile. Bile contains Bilirubin and Bile salts.
2. Maintenance of Blood Sugar – It converts glucose into glycogen and stores it.
3. Regulation of protein metabolism.
4. Regulation of fat metabolism.
5. Formation of ketone bodies.
6. Formation of Plasma Proteins. Synthesis of albumin, prothrombin and fibrinogen solely occurs in the liver.
7. Detoxification of many metabolic products and toxic substances.
8. Erythropoiesis – In fetal life and in anemic conditions, it performs the function of blood formation.
9. Blood coagulation and storage of Vitamin B12 and fat-soluble vitamins A, D, E, K.

Indications for Liver Function Tests:

LFTs are advised in the following conditions:

1. To confirm the diagnosis of liver disease based on clinical signs and symptoms and to know the type of liver disease.
2. For Differential Diagnosis of Jaundice – To differentiate between Surgical Jaundice and Medical Jaundice. It helps to find the exact cause of jaundice when clinically not clear.
3. To detect hepatic insufficiency.
4. To assess the progress of liver disease – whether it is increasing or decreasing.
5. Before prescribing certain drugs that are contraindicated if liver functions are disturbed.
6. It is important to perform multiple tests, as doing only one test can give a “False Positive” or “False Negative” result.

General Indications include:

• Diagnosis of subclinical or mild jaundice.
• Differential diagnosis of jaundice i.e. whether the jaundice is pre-hepatic, post-hepatic or hepatic.
• Evaluation of the degree of damage to the liver.
• To establish the etiology of the disease if possible.

Classification of Liver Function Tests:

Liver function tests can be divided as:

1. Tests based on the excretory functions of the liver.
2. Tests based on metabolic functions of the liver.
3. Determination of the activity of serum enzymes which reflect the activity of the liver.
4. Tests based on the detoxification function.

Important Liver Function Tests:

Based on the above, the important tests are:

1. Serum Bilirubin Estimation
2. Serum Enzymes (SGOT, SGPT and Alkaline Phosphatase)
3. Serum Proteins
4. Prothrombin Time
5. Bromosulphthalein Excretion Test
6. Blood Ammonia
7. Thymol Turbidity Test
8. Liver Biopsy

Note: Tests No. 5, 6, 7 (Bromosulphthalein, Blood Ammonia, Thymol Turbidity) are not used in modern clinical practice nowadays. Liver Biopsy is considered the most definitive test.

Disclaimer:

This content is for educational purposes only and is based on standard medical textbooks. It is not a substitute for professional medical advice. Please consult a qualified doctor for diagnosis and treatment.