1. Hepatic Function Analysis Clinical Pathology January 13, 2009

2. Hepatic Functions Liver is the largest internal organ Complex in terms of structure, function and pathology Multitude of functions include: Metabolic liver functions Key role in conjugation and excretion of bilirubin and bile acids, exogenous drugs, production of proteins, metabolism of amino acids, carbohydrates and lipids and conversion of ammonia to urea. Synthesis: albumin, cholesterol, plasma protein, clotting factors. Digestion & Absorption: related to bile Elimination/detoxification: toxins & catabolism of drugs.

3. Metabolic Functions continued All functions are by enzymatic reactions Malfunctions result in: Jaundice Hypoalbuminemia Hemostasis problems Hypoglycemia Hyperlipoproteinemia Hepatoencephalopathy

4. Enzymes Associated with Hepatocellular Damage Hepatocytes are damaged and enzymes leak into the blood. No single test is superior to any other for detecting hepatic disease although some tests are better at verifying liver function. Hepatocytes are cuboidal to polyhedral cells and or often binucleated.

5. Terminology Microhepatica: small liver, suggests PSS or fibrosis, cirrhosis. Hepatomegaly: enlarged liver, suggests neoplasia, toxicity, systemic disease. Hepatic Encephalopathy: Increased levels of blood ammonia causing severe behavioral changes. Icterus: Yellow discoloration of the skin and/or serum.

8. Alanine Aminotransferase (ALT) Formerly known as SGPT. Dogs, cats, non-human primates major source is the hepatocyte. Horses, ruminants, and pigs not liver specific. Other sources: Renal, cardiac, skeletal muscle and pancreas. Screening test: not precise enough to identify specific liver disease due to other sources. Tests hepatocyte membrane integrity. No correlation between blood levels and severity of hepatic damage. Sample handling: avoid hemolysis & lipemia.

9. Alkaline Phosphatase (Alkphos or AP) As isoenzymes in osteoblasts, chondroblasts, & hepatocellular cells Young animals found in osteoblasts and chondroblasts due to active bone development. Other animals most alkphos is from the liver. Used to detect cholestasis in dogs and cats (not useful in cattle and sheep) Levels will increase with corticosteroid use and Cushing’s Any increase is considered significant in the cat 3x increased levels may be normal in puppies less than 6 months of age.

10. Aspartate Aminotransferase (AST) Formerly known as SGOT. Found in mitochondrial membranes Not liver specific, found in erythrocytes, cardiac muscle, kidneys and pancreas. Increased blood level may indicate nonspecific liver damage. May indicate strenuous exercise or IM injections, muscle inflammation and/or hemolysis. If elevated, check plasma sample for hemolysis or spin hematocrit tube to check. Hemolysis and lipemia may elevate AST (equine has much higher level tha other species)

11. Sorbitol Dehydrogenase (SD) Primary source is the hepatocyte Used in all animals Sheep, goats and swine do not have diagnostic levels of ALT so SD is used in place. Liver specific test for hepatocellular damage or necrosis Disadvantages: unstable in serum & must be assayed within 12 hours of collection. Hemolysis does not affect results.

12. Gamma Glutamyltranspeptidase (GGT) Found in many tissues, primary source is the liver. Kidneys, pancreas, intestines and muscle cells. Elevated with liver disease, especially obstructive liver disease. Cattle, horses, sheep & goats have higher GGT than dogs and cats. Hemolysis has no affect on results. Possibly more specific for hepatic disease in cats. Associated with cholestatis.

13. GGT continued Important marker of hepatobiliary disorders in large animals. High levels are usually found in suckling neonatal young animals. Stable, large enzyme. On rare occasions can be used to diagnose renal tubular disease. Reliable indicator in large animal species of damage to liver and biliary obstruction.

14. Albumin Made in liver Maintains blood volume and binds to hormones May be lost through the gut or kidneys. Low levels may also indicate maldigestion or malabsorption.

15. Liver Function Dye Excretion BSP clearance Sulfobromophthalein (BSP) Dye injected IV and retrieved by the liver, conjugated and exreted in the bile. Blood is drawn 30 minutes later Disappearance from the plasma depends on hepatic blood flow, bile flow and hepatocellular integrity. Horses it is used to differentiate hepatic jaundice from anorexia & hepatoencephalopathy. Cattle for fascioliaiss, liver abscess, ketosis, and liver flukes. Swine Aflatoxocosis Hepatic lesions delay BSP excretion & indicate a loss of at least 55% of liver’s functional mass.

16. Indocyanine Green Clearance (ICG) Used to estimate hepatic blood flow. Poor availability of test IV injection in horses, dogs and cats 5-6 plasma samples at 0, 5, 10, 15, & 30 minutes post injection. ICG concentration measured photometrically and half-life determined. Measure clearance rate at 0, 5, 10, & 15 minutes. Delayed in hepatic blood flow shows hepatic necrosis & bile duct obstruction.

17. Ammonia Tolerance Liver disease may impair ammonia detoxification leading to hepatoencephalopathy. Ammonium chloride orally or rectally Used to detect abnormal portal blood flow. Usually measured in heparinized blood sample. May cause vomiting or CNS signs.

18. Prothrombin Time (PT) Prothrombin is a Vitamin K dependent coagulation factor made by the liver. Activated by tissue thromboplastin and calcium. Initiates the coagulation involving liver coagulation factors I, II, V, VII, & X but most especially VII. Indicates coagulation factor insufficiency & possible liver necrosis, cirrhosis or poor bile secretion which is necessary for Vitamin K absorption.

19. Bile Acid Concentrations Synthesized by hepatocytes from cholesterol & conjugated with glycine or taurine. Serum bile acid (SBA) elevated with any process that impairs the hepatocellular, biliar or portal enterohepatic circulation of bile acids. Hepatic insufficiency results in an inability to extract bile acids from the blood.

20. Bile Acid Measurements Bile acids are made by the liver. The bile acids are secreted into the gut after eating. Fast animal 12 hours, take preprandial sample, feed animal moderately fatty meal, then take postprandial blood sample 2 hours later.

21. Bilirubin A metabolite of heme portion of Hemoglobin, a waste product when RBC lyses. Liver conjugates to water soluble then converted to urobilinogen by bacterial enzymes- urobilinogen eliminated by kidneys and in the feces. Both unconjugated and conjugated bilirubin in plasma=total bilirubin Conjugated referred to as direct because measured directly. Icterus: detectable in the sclera at levels 3-4 mg/dl, detectable in the serum at 1.5-2 mg/dl. Normal values are less 1.0 mg/dl for dogs and cats. Any increase in the serum bilirubin over normal is considered significant in dogs and cats. Horses may become icteric if anorexic.