Liver function test by nilesh sharma
- 1. Liver function test BY- NILESH SHARMA (PHARM.D 1ST YEAR)
- 2. • Liver performs several diversified functions. lt is the central organ of body's metabolism. Functions of liver • 1 . Metabolic functions : Liver actively participates in carbohydrate, lipid, protein, mineral and vitamin metabolisms. • 2. Excretory functions : Bile pigments, bile salts and cholesterol are excreted in the bile into intestine. • 3. Protective functions and detoxification : Kupffer cells of liver perform phagocytosis to eliminate foreign compounds. Ammonia is detoxified to urea. Liver is responsible for the metabolism of xenobiotics (detoxification). • 4. Hematological functions : Liver participates in the formation of blood (particularly in the embryo), synthesis of plasma proteins (including blood clotting factors) and destruction of erythrocytes. • 5. Storage functions : Clycogen, vitamins A, D and 812 and trace element iron are stored in liver.
- 3. Tests to assess liver function • The liver function tests (LFT) are the biochemical investigations to assess the capacity of the liver to carry out any of the functions it performs. • LFT will help to detect the abnormalities and the extent of liver damage.
- 4. The major liver function tests may be classified as follows • 1. Tests based on excretory function: Measurement of bile pigments, bile salts, bromosulphthalein. • 2. Tests based on serum enzymes derived from liver: Determination of transaminases, alkaline phosphatase, 5'-nucleotidase, y-glutamyl transpeptidase. • 3. Tests based on metabolic capacity -Galactose tolerance, antipyrine clearance. • 4. Tests based on synthetic functions -Prothrombin time, serum albumin. • 5. Tests based on detoxification-Hippuric acid synthesis.
- 6. Markers of Liver Function • BILIRUBIN: Bilirubin is a bile pigment, and is the excretory end product of heme degradation. lt is conjugated in the liver to form bilirubin di- glucuronide, and excreted in bile. • Serum bilirubin: The normal concentration of serum bilirubin is in the range of 0.2-1 mg/dL Of this, the conjugated bilirubin(di-glucuronide 75%,monoglucuronide 25%) is about 0.2-0.4 m/dl, while the unconjugated bilirubin is 0.2-0.6 mgldl.
- 7. • Icterus index: This is a simple test to measure the yellow color of serum due to bilirubin. • This test is rather crude and almost out dated. • However, it is often useful for a rapid assessment of neonatal jaundic.
- 8. van den Bergh reaction • This is a specific reaction to identify the increase in serum bilirubin. • Normal serum gives a negative van den Bergh reaction. • Mechanism of the reaction : van den Bergh reagent is a mixture of equal volumes of sulfanilic acid (in dilute HCI) and sodium nitrite. The principle of the reaction is that diazotised sulfanilic acid (in the above mixture) reacts with bilirubin to form a purple coloured azobilirubin. • Direct and indirect reactions : 1. Bilirubin as such is insoluble in water while the conjugated bilirubin is soluble. van den Bergh reagent reacts with conjugated bilirubin and gives a purple colour immediately (normally within 30 seconds). This is referred to as a direct positive van den Bergh reaction. 2. Addition of methanol (or alcohol) dissolves the unconjugated biliruhin which then gives the van den Bergh reaction (normally within 30 minutes) positive and this is referred to as indirect positive. 3. lf the serum contains both unconjugated and conjugated bilirubin in high concentration, the purple colour is produced immediately (direct positive) which is further intensified by the addition of alcohol (indirect positive). This type of reaction is known as biphasic. • Van den Bergh reaction and jaundice : This reaction is highly useful in understanding the nature of jaundice. This is due to the fact that the type of jaundice is characterized by increased serum concentration of unconjugated bilirubin (hemolytic), conjugated bilirubin (obstructive) or both of them (hepatic). • Therefore, the response of van den Bergh reaction can differentiate the jaundice as follows – Indirect positive - Hemolytic jaundice – Direct positive - Obstructive jaundice – Biphasic - Hepatic jaundice
- 9. Bilirubin in urine • The conjugated bilirubin, being water soluble, is excreted in urine. This is in contrast to unconjugated bilirubin which is not excreted. • Bilirubin in urine can be detected by Fouchet's test or Gmelin's test. • Gmelin's test is a chemical test used for detecting the presence of bile pigments in urine. 5ml of urine is slowly added to 5ml of concentrated nitric acid in a test-tube. • Different coloured rings between the two layers are visible if bile pigments are present as they are oxidised to various chemical products. Nitric acid is used as the oxidising agent. • Blue, green and violet rings are seen if bilirubin is present. • Gmelin's test is not sensitive so a positive result always indicates the presence of bile pigments but a negative result does not exclude the presence of small quantities of bile pigments.
- 10. Fouchet's test : • To 5 ml of urine add 1 ml of 10% barium chloride (BaCl2). • This should form barium sulphate precipitate and if it does not, add a few drops of saturated ammonium sulphate. • Add a drop of Fouchet's reagent to the precipitate formed. • A green or blue color is formed if positive.
- 11. Bromosulphthalein (BSP) test • Bromosulphthalein is a dye used to assess the excretory function of liver. • lt is a non-toxic compound and almost exclusively excreted by the liver (through bile). • BSP is administered intravenously (5 mg/kg body weight) and its serum concentration is measured at 45 min and at 2 hrs. • In normal individuals, less than 5% of the dye is retained at the end of 45 min. • Any impairment in liver function causes an increased retention of the dye. • This test is quite sensitive to assess liver abnormality with particular reference to excretory function.
- 12. SERUM ENZYMES DERIVED FROM LIVER • Liver cells contain several enzymes, which may be released into the circulation in liver damage. • Measurement of selected enzymes in serum is often used to assess the liver function. • Some of these enzymes are discussed hereunder.
- 13. Transaminases or aminotransferases • The activities of two enzymes namely- • serum glutamate pyruvate transaminase (SGPT; recently called as alanine transaminase-ALT) • serum glutamate oxaloacetate transaminase (SGOT; recently known as aspartate transaminase- AST ) -are widely used to assess the liver function. • ALT is a cytoplasmic enzyme while AST is found in both cytoplasm and mitochondria. The activity of these enzymes is low in normal serum (ALT 5-40 lU/l; AST 5-45 lU/l). • Serum ALT and AST are increased in liver damage. However, alanine transaminase is more sensitive and reliable for the assessment of LFT.
- 14. Alkaline phosphatase • Alkaline phosphatase (ALP) is mainly derived from bone and liver (the cells lining the bile canaliculi). • A rise in serum ALP (normal 3-13 KA units/dl), usually associated with elevated serum bilirubin is an indicator of biliary obstruction (obstructive/pos- thepatic jaundice). • ALP is also elevated in cirrhosis of liver and hepatic tumors.
- 15. γ - Glutamyl transpeptidase • This is a microsomal enzyme widely distributed in body tissues, including liver. • Measurement of y-glutamyl transpeptidase (GGT) activity provides a sensitive index to asses liver abnormality. • The activity of this enzyme almost parallels that of transaminases in hepatic damage. • Serum GGT is highly elevated (normal 5-4O lU/I )in biliary obstruction and alcoholism. • Further, several drugs (e.g. phenytoin) induce (liver synthesis) and increase this enzyme in circulation.
- 16. 5'-Nucleotidase • The serum activity of 5'-nucleotidase (normal 2-15 U/l) is elevated in hepatobiliary disease and this parallels ALP. • The advantage with 5'-nucleotidase is that it is not altered in bone disease (as is the case with ALP).
- 17. Other enzymes • Serum isocitrate dehydrogenase and isoenzymes of lactate dehydrogenase (LDH4 and LDH5) are also useful in LFT.
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