Liver Function PDF

Clinical Pathology Dr. Wisam Salim Hassan Liver Function The liver is an organ of many diverse metabolic activities and any assessment of its functional status is dependent upon its ability to perform a specific metabolic function. Estimation of the...

Clinical Pathology Dr. Wisam Salim Hassan Liver Function The liver is an organ of many diverse metabolic activities and any assessment of its functional status is dependent upon its ability to perform a specific metabolic function. Estimation of the presence or absence of hepatic malfunction is further complicated by the tremendous functional reserve of the. liver and its powers of regeneration. Also, the various functions of the liver may be altered unequally by hepatic disease. Indications For Liver function Tests: 1. Assist in the differential diagnosis of icterus resulting either from a hemolytic crisis or from an extrahepatic or intrahepatic obstruction of the bile duct system 2. In primary liver diseases that are present either with or without icterus for example, infectious hepatitis or suppurative hepatitis 3. In secondary liver disorders such as chronic passive congestion, infiltrative and degenerative lipidoses 4. In the prognosis of hepatic disease , and the evaluation of therapy Limitations of Liver Function Tests: 1. Extensive damage is required before tests show impaired function because of the great reserve power of the liver 2. The tests are lacking sensitivity or are too sensitive 3. There are so many functions of the liver that testing one does not indicate the function status of the entire organ 4. Specific hepatic functions are greatly affected by a wide variety of pathologic conditions of extrahepatic origin Clinical Pathology Dr. Wisam Salim Hassan Classification of Liver Function Tests: 1. Tests dependent primarily on hepatic secretions and excretions A. Bile pigments B. Clearance of foreign substances 2. Tests dependent upon specific biochemical functions A. Protein metabolism tests B. Carbohydrate metabolism tests C. Lipid metabolism tests 3. Tests dependent upon the measurement of serum enzyme activity A. Transaminases B. Alkaline phosphatase C. Other enzymes Tests dependent primarily on hepatic secretions and excretions Bile pigments Serum Bilirubin: The chief bile pigment found in the serum of animals is Bilirubin. Bilirubin may exist in two forms: as a protein-bound substance in plasma, and as a conjugate known as Bilirubin glucuronide The determination of total Bilirubin and conjugated Bilirubin in serum is based on the van den Bergh reaction. This test is based on the ability of bilirubin to couple with diazobenzosulfochloride (diazo reagent) to form a characteristic red-violet pigment. The reaction requiring the addition of alcohol to the serum reagent mixture is called the “indirect reaction”, and it is a specific test for unconjugated bilirubin. The direct reaction is a specific test for conjugated bilirubin Indications for Serum Bilirubin determination: Classifying icterus in a diseased animal and also to measure the response of the liver to therapy and thus assist in making accurate prognosis. Clinical Pathology Dr. Wisam Salim Hassan Bile pigments in urine: Urinary Urobilinogen: It refers to all substances reacting positively with Ehrlich’s reagent. These pigments are produced by bacterial reduction of bilirubin conjugates in the intestine where they are partly absorbed into the total circulation and partly recycled. Fecal bile pigments: Fecal bilirubin appears in conditions that prevent the reduction of bilirubin to Urobilinogen this occurs in following: 1) In diarrhea 2) As a result of suppression of bacterial action 3) In the newborn receiving milk The urobilinoid pigments similar to those observed in the urine are normally present in feces, and the predominant pigment is stercobilin. Clearance of Foreign Dyes from the Serum: The clearance of a foreign dye from the serum following parenteral injection is a measure of both biochemical integrity and blood flow in the liver. Dyes that have been used in veterinary medicine include: Sulfobromophthalein (Bromosulphalein (BSP)), rose Bengal, indocyanine green (ICG), and Phenoltetrachlorophtalein Sulfobromophthalein: The BSP clearance test is a widely used index of hepatic function in domestic animals. indocyanine green (ICG): It has been recommended for use in dogs to determine the functional status of the liver Clinical Pathology Dr. Wisam Salim Hassan Tests based on specific biochemical functions: Plasma proteins: which include Albumin, globulins, fibrinogen, glycoproteins, lipoproteins Indications for determining plasma proteins: 1. Estimation of the nutritional state of the animal, and it also reflect alterations in metabolism 2. Alterations in plasma protein concentration may be indicative of disease 3. It assists in the diagnosis and prognosis of cases associated with liver and kidney diseases 4. It serves as a guide in the administration of fluids during an emergency such as shock, dehydration , and hemorrhage
Total plasma proteins can be determined by refractometric method and Biuret method Protein Metabolism Tests of Liver Function: Serum Albumin and Globulins Coagulation factors Amino acid tolerance test Blood ammonia Tests Based on Serum Enzyme Activity: Alterations in serum enzyme activity due to malfunctioning of the liver occur as a result of: 1. An elevation of enzymes due to disruption of hepatic cells as a result of necrosis. These enzymes include: alanine amino transferase (ALT), aspartate amino transferase (AST), glutamic dehydrogenase (GD), lactic dehydrogenase (LDH) 2. A decrease in concentration in the serum resulting from impaired synthesis by the liver (Choline esterase) 3. An elevation in enzyme levels due to cholestasis, alkaline phosphatase (AP), γ-glutamyl transferase (GGT), and leucine aminopeptidase (LAP) Clinical Pathology Dr. Wisam Salim Hassan Transaminases (Amino Transferases) The two clinically important Amino Transferases are alanine amino transferase (ALT), aspartate amino transferase (AST). Indication for test: Tests for levels of serum ALT are of value in detecting liver disease in dogs, cats and primate. ALT is increased in serum when cellular degeneration or destruction occurs in liver. AST is present in all tissues of the body, it is not an organ-specific test and may be utilized to detect destruction in a wide variety of tissues. This enzyme is present in extremely high concentrations in muscle both skeletal and cardiac. Serum AST levels may be increased with liver disease in all species but cannot be considered to be a specific test for liver damage. Liver Biopsy A liver biopsy is a procedure in which a small needle is inserted into the liver to collect a tissue sample. Indications: 1. Malignant hepatic neoplasms 2. Suspected fibrosis 3. Obscure liver disease 4. Metabolic diseases such as amyloidosis, and lipidoses 5. Heavy metal intoxications by arsenic, molybdenum, or selenium