Liver function tests (LFTs) are group of clinical biochemistry laboratory blood assays performed to give information about the state of a patient's liver. They are useful in the evaluation of functionality and the cellularity of liver.  It is also useful in assessing the condition if the biliary system.  They are also useful in the management of patients’ hepatic dysfunction.

Sample needed for the test

The test is performed on a patient's serum or plasma sample. The sample is collected by the phlebotomist from the patients vein.

Purpose of LFT

These tests are used to

1. To detect the presence of liver disease.
2. To distinguish among different types of liver disorders.
3. To gauge the extent of known liver damage.
4. To follow the response to treatment.

Components of LFT and uses

• Alanine transaminase (ALT), OR Serum Glutamic Pyruvate Transaminase(SGPT) is an enzyme present in hepatocytes (liver cells). ALT is raised in acute liver damage, such as viral hepatitis or liver toxicity secondary to drugs.  Normal values: 5 to 40 IU/L.
• Aspartate transaminase (AST) OR Serum Glutamic Oxaloacetic Transaminase (SGOT) is another enzyme present in hepatocytes. It is also seen in other cells like red blood cells, cardiac and skeletal muscle.  It is raised in acute liver damage. It is also used as cardiac marker. The ratio of AST to ALT is sometimes part of LFT. It helps in differentiating the causes of liver damage.    Normal values: 10 to 40 IU/L
• Alkaline phosphatase (ALP) is an enzyme in the cells lining the biliary ducts of the liver. Conditions associated with raised ALP levels are large bile duct obstruction, intrahepatic cholestasis or infiltrative diseases of the liver. ALP is also present in bone and placental tissue, so it is higher in growing children and elderly patients with Paget's disease.     Normal values: 30 to 120 IU/L
• Bilirubin is a breakdown product of heme (a part of hemoglobin in red blood cells). Increase in bilirubin causes jaundice.  There are present in two forms Direct OR Conjugated bilirubin and Indirect OR Unconjugated bilirubin, LFT include

      a)Total bilirubin (both Direct and Indirect bilirubin) which indicates a number of problems as follows

1.  Prehepatic causes: Hemolytic anemias and internal hemorrhage.
2.  Hepatic causes: Cirrhosis and viral hepatits
3.  Posthepatic causes: Obstruction of the bile ducts either within the liver or in the bile duct.  Normal values: 0.1 - 1.2mg/dl

      b) Direct bilirubin is used to narrow down the diagnosis of jaundice.

1. If direct bilirubin is normal then Hemolysis, viral hepatitis, or cirrhosis can be suspected.
2. If it is elevated then Bile duct obstruction by gallstones or cancer should be suspected.    Normal values: 0 - 0.3 mg/dL

• Gamma glutamyl transpeptidase (GGT) is an enzyme marker for cholestatic damage. They are more sensitive than ALP. GGT is raised in alcohol toxicity both acute and chronic.
• Albumin and total protein: Levels of albumin, a protein made by the liver and total protein indicates how well your liver is making proteins that your body needs to fight infections and perform other functions. Lower than normal levels are seen in  liver damage or disease. Albumin value: 3.5 to 5.0 grams per deciliter ,total protein value:6.3 to 7.9 g/dL
• Other parameters which are checked as a part of LFT are

1. 5' nucleotidase is another test specific for cholestasis or damage to the intra or extrahepatic biliary system.  They are used as a substitute for GGT
2. Coagulation tests include prothrombin time, activated prothrombin time and International Normalized Ratio (INR) measures the speed of coagulation comparing it to normal.
3. Lactate dehydrogenase is an enzyme found in many body tissues, including the liver. Elevated levels of LDH may indicate liver damage.

Normal values and Reference range

1. Alanine transaminase OR Serum Glutamic Pyruvate Transaminase: 5 to 40 IU/L.
2. Aspartate transaminase OR Serum Glutamic Oxaloacetic Transaminase: 10 to 40 IU/L
3. Alkaline phosphatase (ALP): 30 to 120 IU/L
4. Total Bilirubin: 0.1 - 1.2mg/dl
5. Direct bilirubin: 0 - 0.3 mg/dL
6. Gamma glutamyl transpeptidase (GGT):0 to 51 IU/L
7. Albumin: 3.5 to 5.0 g/dl
8. Total protein value: 6.3 to 7.9 g/dL
9. LDH: 122 to 222 micromoles per liter (mcmol/L)