Hepatic Functions. and. Laboratory Assessment. Serkan SAYINER, DVM PhD. Assist. Prof.

Transcription

1 Hepatic Functions and Laboratory Assessment Serkan SAYINER, DVM PhD. Assist. Prof. Near East University, Faculty of Veterinary Medicine, Department of Biochemistry

2 Liver Liver is the major organ that regulates too many metabolic reactions. It is also called Metabolic Chief. It s regeneration ability is quite high. A liver that is only 10-20% functional is sufficient for survival. Complete removal of the organ results in death within 24 hours. It consists of, Hepatocytes (%60), Reticuloendothelial cells (Kupffer) and sellate cells (Ito cells) (%30), Basolateral membrane (surface) - sinusoids, Blood circulation apical (canalicular) membrane bile duct (%10).

3 Liver Molecules found in liver %76 water %16 protein %5-10 glycogen %2,2 lipids Anatomic structures Hepatic cells, bile duct system, vascular siystem and reticuloendothelial system Blood flow is provided by portal vein, hepatic arteryveina and capillary fenestrations.

4 Metabolic Functions Carbohydrate Metabolism Gluconeogenesis Glycogenesis, glycogenolysis Lipid Metabolism Fatty Acid synthesis Cholesterol synthesis and excretion Lipoprotein synthesis Ketogenesis Synthesis of Bile Acids 25-hydroxylation of vitamin D

5 Metabolic Functions Protein Metabolism Synthesis of plasma proteins Coagulation factors, immunglobulins, albumin, cytokines Ure Synthesis Hormone Metabolism Synthesis and exceetion of steroid hormones Metabolims of polypeptide hormones Metabolism and disposal of drugs and foreign substances (Detoxification)

6 Metabolic Functions Bilirubin metabolism and its excretion Nucleic acid metabolism It is involved in the Purine and pyrimidine synthesis. It's rich in xanthine oxidase. Storage Function Glycogen Vitamin A Fe

7 Liver Diseases Liver pathologies include primary hepatic cells, bile duct and vascular system. Functional tests show mostly cellular injury and response to cellular disorders. The great majority of the disorders are pathologically present in the form of liver cell necrosis, intrahepatic and extrahepatic bile duct obstruction (cholestasis), liver atrophy and/or liver fibrosis.

8 Hepatocellular Injury Hepatocyte injury is determined by measuring hepatocellular enzyme activities (leakage enzymes). 3 enzymes are used routinely. These are ALT, AST, SDH In addition, GLDH is available.

9 Hepatocellular Injury ALT It is ap primary marker of hepatocellular damage. Especially in cats and dogs. Increased activity express hepatocyte death, sublethal hepatocyte damage. ALT activity is sometimes the only test used to detect hepatocyte injury in dogs and cats Apart from the liver, it is also found in the skeletal and heart muscles. CK should be evaluated for differential diagnosis. Horses and ruminants have low ALT concentration in hepatocytes; consequently, serum ALT activity is not useful for detecting liver disease in these species

10 Hepatocellular Injury Moderate amounts of ALT are present in the muscle of horses and ruminants, and moderate increases in the serum ALT activity occur with muscle injury in these species; however, ALT is not included in large animal biochemical profiles. Other muscle-specific enzymes (e.g., CK) are more commonly used for detecting muscle injury in these species. In dogs and cats, a wide variety of liver diseases can produce increased serum ALT activity. Hypoxia, metabolic alterations resulting in hepatocyte lipid accumulation, bacterial toxins, inflammation, hepatic neoplasia, and a multitude of toxic chemicals and drugs can cause hepatocyte injury, thereby resulting in ALT leakage.

11 Hepatocellular Injury Acutely, the serum activity of ALT is proportional to the number of cells that are injured But the magnitude of ALT activity is not indicative of the cause of the injury. After acute severe injury, such as from a toxin, serum ALT activity can increase markedly within a day or two. If the injury is not ongoing, ALT activity slowly decreases over several weeks. There is also an increase during active hepatic regeneration. Although the half-life is hours in dogs and 3.5 hours in cats, it is consistently high in recovery.

12 Hepatocellular Injury In chronic inflammatory conditions, ALT activities are fluctuating. Result in periodic flares of increased ALT activity Repetitive measurements should therefore be made. Thus, a deeper assessment of the disease can be made. It is important to recognize that in certain situations significant liver disease can occur with normal or only slightly increased serum ALT activity. If hepatic mass is markedly decreased. Massive acute hepatic necrosis Aflatoxin

13 Hepatocellular Injury Increases in serum ALT activity can also be observed in dogs with hyperadrenocorticism or that have been administered corticosteroids. These increases are generally mild (two- to fivefold), but ALT activity increases can vary widely among dogs receiving corticosteroid therapy, depending on the dose and duration of treatment. Anticonvulsant drugs (e.g., phenobarbital) also cause mildly increased serum ALT activity in dogs. Some dogs receiving anticonvulsants will develop a toxic hepatopathy, in which case ALT activity may be markedly increased

14 Hepatocellular Injury AST It is present at highest concentrations in hepatocytes and muscle cells (both skeletal and cardiac) of all species. Therefore, AST is not a liver-specific enzyme. AST is found predominantly in the cytoplasm. With about 20% located within mitochondria. Increased serum AST activity can result from lethal or sublethal injury to either hepatocytes or muscle cells. In dogs and cats with liver diseases, serum AST activity will generally increase parallel to ALT activity, but the magnitude of the increase may be less than that of ALT.

15 Hepatocellular Injury The serum AST activity may return to baseline faster than ALT following acute liver injury in some animals, making repeated measurements useful for monitoring disease resolution. Although AST is less liver specific than ALT, it may be more sensitive than ALT for detecting some liver diseases (e.g. Hepatic lipidosis in cats). Similar to ALT, mild increases in AST activity may be seen in dogs as a result of enzyme induction due to corticosteroids and possibly phenobarbital. CK activity measurement should be done for differential diagnosis (for muscle).

16 Hepatocellular Injury In horses and ruminants, it is routinely used (more frequently) in the assessment of hepatocellular damage and is absolutely within the biochemical profiles. Yinede spesifitesinin sadece karaciğer ait olmaması nedeniyle tek başına yeterli değildir. Ayırıcı tanı için CK ölçülmelidir. The major problem with AST in detecting hepatocyte injury is its lack of liver specificity. CK should be measured for differential diagnosis. Increased AST activity with normal CK activity may be seen if the source of the AST is the liver, suggesting hepatocyte injury has occurred. The half-life of CK is shorter than that of AST. Serum activities of both enzymes may increase as a result of muscle injury, but the CK activity may return to normal earlier than the AST activity. These problems with use of AST in detecting hepatocyte injury in horses and ruminants have led to use of more liver-specific enzymes (such as sorbitol dehydrogenase [SDH]) in these species.

17 Enzyme Activity Serum activities of both AST and CK increase because of muscle injury. CK AST 24 A Hours since injury

18 Hepatocellular Injury SDH It is free in the cytoplasm. It is liver specific enzyme in dogs, cats, horses and ruminants. Increased serum SDH activity is suggestive of either hepatocyte death or sublethal hepatocyte injury. It is not used very often in cats and dogs. In horses and ruminants, SDH is much more specific than AST. Thus, it is preferable to AST for detecting hepatocyte injury in horses and ruminants The half-life of SDH is very short; serum activities may return to normal within 4 5 days after acute hepatocyte injury. The main disadvantage to SDH is that it is less stable in vitro than most other diagnostic enzymes

19 Hepatocellular Injury GLDH It plays a key role in the detoxification of ammonia. It is a leakage enzyme present in highest concentration within mitochondria of hepatocytes. Liver specific for horse and ruminants (hepatic necrosis). Used in dogs and cats. No analysis is done in each laboratory. Increased serum concentration is reported to have excellent sensitivity for the detection of canine hepatic disease. Serum activity of GLDH may increase in dogs with hyperadrenocorticism; increases have also been documented in dogs receiving anti-convulsants.

20 Cholestasis Cholestasis (impaired bile flow) can be detected by measuring the activities of serum enzymes whose increased production is induced by cholestasis or by measuring the serum concentrations of substances. ALP It is attached to cell membranes and synthesized by many tissues such as liver, bone, kidney, intestine, pancreas, and placenta. Most of the normal serum ALP activity originates from the liver. The half-life of other isoenzymes is short. Increased serum ALP activity commonly occur with cholestasis, increased osteoblastic activity, induction by certain drugs (primarily in dogs), and a variety of chronic diseases.

21 Cholestasis ALP in the liver is associated with biliary epithelial cells and canalicular membranes of hepatocytes. A variety of hepatobiliary diseases can result in increased serum ALP activity due to increased enzyme production, solubilization of membranes by the action of bile salts, and release of membrane blebs after cell injury. Cholestatic diseases can result in marked increases in serum ALP activity in dogs (greater than 10 fold), but increases are more variable in other species.

22 Cholestasis The half-life of the cholestasis-induced ALP is approximately 3 days in dogs but only 6 hours in cats. However, ALP is still a useful enzyme for evaluation of feline cholestatic liver disease if one keeps in mind that even mild increases (2 3 URL) can be significant. The utility of ALP for detection of cholestasis in horses and ruminants is generally considered inferior to that of GGT. When cholestasis is the cause of increased serum ALP activity, serum total bilirubin and bile acid concentrations may be increased concurrently.

23 Cholestasis In dogs with cholestasis, serum ALP activity often increases prior to increases in serum bilirubin concentration; thus ALP is a more sensitive indicator. However, even if the serum bilirubin concentration is normal, bilirubinuria may accompany cholestasisinduced increases in ALP. Whereas lesions primarily involving the intra- or extrahepatic biliary system are common causes of cholestasis, hepatic diseases resulting in significant hepatocyte swelling (e.g., lipidosis or inflammation of the hepatic parenchyma) can obstruct small bile canaliculi and induce increased ALP production and release.

24 Cholestasis Increased serum ALP activity associated with increased osteoblastic activity occurs in all species. These increases are most often detected in young, growing animals. E.g. the reference interval for total ALP activity in four-week old kittens was U/L compared to U/L for adult cats. One must remember that young animals commonly have serum ALP activities greater than adult reference intervals. In puppies, kittens, and calves, ALP activity increases attributed to bone growth are generally mild (<4 5 ), but foals may have increases up to 20 in the first three weeks of life.

25 Cholestasis In mature animals, oosteosarcoma and other bone neoplasms (both primary and secondary) inconsistently result in increased serum ALP activity. Fracture healing usually results in localized increases in osteoblastic activity and mild increases in serum ALP that may be useful for monitoring the progression of healing. Canine hyperparathyroidism (primary or secondary) and feline hyperthyroidism may result in increased bone turnover and increased osteoblastic activity; mild increases in serum ALP may be detected in patients with these diseases.

26 Cholestasis Serum ALP activity can be markedly increased when enzyme production is induced by certain drugs. Corticosteroids (exogenous or endogenous) and anticonvulsants induce increased ALP production by canine hepatocytes. Increased serum ALP activity induced by corticosteroids varies depending on dose and duration of exposure, but can be marked (>20 ). Anticonvulsants generally cause somewhat milder increases (<10 ).

27 Cholestasis Neonates of several species have high serum ALP activity following ingestion of colostrum. During the first few days of life puppies, kittens, and lambs have transient marked increases in serum ALP activity (up to or >30 for adult animals). Hyperadrenocorticism has already been discussed as a cause of often marked corticosteroid-induced ALP activity increases in dogs. Diabetes mellitus, canine hypothyroidism and hyperparathyroidism, and feline hyperthyroidism result in increased ALP activity. Neoplasia may be associated with increased serum ALP activity (Hepatic, mammary gland, bone).

28 Increased Serum ALP activity in dogs NO Young growing dog? YES Serum Bilirubin (hemolysis) Bilirubinuria Serum Bile Acids Are any of these increased? YES NO YES ALP >3x? NO Consider Bone ALP from osteoblastic activity Consider hepatobiliary diseases and perform additional tests Liver Function Tests Tests for pancreatic injury Radiology Ultrasound Liper biopsy Abdominal fluid evaluation Is dog receiving corticosteroids or anticonvulsants? YES Consider drug induction of ALP. Source: Thrall et al., 2012 NO YES Evidence of bone disease and ALP <3x? NO Evaluate adrenocortical function

29 Cholestasis GGT It is considered an induced enzyme. Most body tissues synthesize GGT, with the highest concentrations occurring in the pancreas and kidney. Most of the serum GGT activity originates in the liver. Release from renal epithelial cells results in increased urinary GGT activity, but not increased serum GGT activity. Similarly, pancreatic cells release GGT into pancreatic ducts rather than into the blood. Increased GGT production, release, and subsequent increased serum GGT activity occur with cholestasis and biliary hyperplasia. In dogs, increased GGT activity also occurs as a result of drug induction. Dogs may show up to 50 fold GGT increase on bile duct obstruction. The cat's up to 16 fold.

30 Cholestasis It should be evaluated with ALP in cats and dogs. E.g. In cats with hepatic lipidosis, ALP increase is more significant than GGT. However, if the root cause of disease is necroinflammatory, GGT activity may be higher than ALP. Similar to ALP, increases in serum GGT activity are seen in dogs receiving corticosteroids. Its activity increases more slowly. Anticonvulsants may also cause an increase in GGT (2-3x). If this increase is much higher, it can be considered to be due to cholestasis rather than drug. Significant increase in drug-induced adverse may be a sign drug-associated toxic hepatopathy that it can be lifethreatening.

31 Cholestasis In horses and cattle, GGT is generally considered more sensitive than ALP for detection of cholestasis. Generally higher than ALP. Biliary hyperplasia and liver failure develop due to alkaloid poisoning in horses and cattle. In this case, the GGT also increases considerably. However, in chronic cases ALP may increase higher than GGT. Cattle with moderate to severe hepatic lipidosis have only mild increases in serum GGT activity. Since there is high GGT activity in the colostrum of dogs, sheep and cattle, serum GGT levels in newborns may increase up to 50 fold. After an average of 5 weeks, they begin to fall to normal levels. It can be used to evaluate passive immunity.

32 Serum GGT Activity in Animals with Hepatobiliary Disorders Species Dog Cat Horse Disorders Bile duct obstruction, chronic hepatitis, lipidosis, necrosis, cirrhosis, neoplasia, corticoid therapy Bile duct obstruction, cholangiohepatitis, cirrhosis, lymphosarcoma, necrosis Toxic hepatic failure, subclinical hepatopathy, hyperlipidemia Cattle Fascioliasis, lipidosis, Metacercariae migrations, Senecio poisoning Sheep Bile duct obstruction, toxicity, fascioliasis,lupinosis, Cobalt deficiency, Ketosis Source: Kaneko et al., 2008

33 Liver Function Tests Tests of liver function include, Measurement of the serum concentrations of substances that normally are removed from the blood by the liver and then metabolized or excreted via the biliary system (e.g., bilirubin, bile acids, ammonia, cholesterol), and substances that normally are synthesized by the liver (e.g., albumin, globulins, urea, cholesterol, coagulation factors).

34 Liver Function Tests Any increase in these substances can also be attributed to non-hepatic causes. However, if there is additional evidence for liver disease and abnormal concentrations are detected, the presence of liver disease or failure may be mentioned. If necessary, the liver biopsy should be done.

35 Source: eclinpath Bilirubin Metabolism BLOOD Extravascular or intravascular hemolysis Unconjugated bilirubin (indirect) + albumin Hepatic sinusoid Unconjugated Bilirubin Urobilinogen HEPATOCYTE Transported with ligandin or Z protein Conjugated to glucuronic acid Conjugated Bilirubin (Direct) Urobilinogen KIDNEY Biliary System Small intestine Conjugated Bilirubin Bacterial proteases %10 Portal vein Urobilinogen or Stercobilinogen %90 Stool Urobilinogen excreted in urine

36 Liver Function Tests Abnormalities of bilirubin metabolism Three main pathologic processes can cause hyperbilirubinemia. 1. Increased bilirubin production (due to accelerated erythrocyte destruction) 2. Decreased bilirubin uptake or conjugation by hepatocytes, 3. Decreased bilirubin excretion (cholestasis). Total Bilirubin = Indirect (Unconjugated) Bilirubin + Direct (Conjugated) Bilirubin

37 Liver Function Tests ICTERUS: Also known as Jaundice, It is a yellowish pigmentation of the skin, sclera and mucous membranes due to high bilirubin levels in blood circulation. 1. Pre-Hepatic Icterus 2. Hepatic Icterus 3. Post-Hepatic Icterus

38 Free Bilirubin Hemoglobin Pre-Hepatic Ikterus -Hemolytc diseases -Internal Hemoraji Glucuronide conjugation Increased serum Indirect Bilirubin Total Bilirubin Conjugated Bilirubin Urobilinogen or Stercobilinogen Urobilinogen Stool (stercobilin) In urine Urobilinogen increases. No bilirubinuria.

39 Hepatic Free Bilirubin Hemoglobin Icterus Glucuronide conjugation -Decreased functional hepatic capacity due (acute/chronic hepatitis) -Hereditary defects -Secondary to fasting (atlarda) -Intrahepatic cholestasis? Conjugated Bilirubin Urobilinogen or Stercobilinogen Urobilinogen Bilirubin glucuronides Stool (stercobilin) Increased serum Total Bilirubin? Indirect bilirubin In urine Bilirubinuria

40 Post-Hepatic Glucuronide conjugation Free Bilirubin Hemoglobin Icterus Intra- or extrahepatic bile duct obstruction (cholestasis) Infections Neoplasm Secondary to small intestine or pancreatic lesions Sepsis Extrahepatic obstruction Bilirubin glucuronides Clay-colored Stool Increased serum Total Bilirubin Direct Bilirubin İdrarda Bilirubinuria Deltabilirubin? Urobilinogen negative/normal

41 Source: Thrall et al., 2012 HYPERBILIRUBINEMIA YES ANEMIC? NO Regenerative? YES NO Is ALP and/or GGT increased? YES NO Is total protein decreased? YES NO Consider anemia secondary to chronic liver disease Cholestasis Hepatic Failure Bile leakage Anorexia (Horses, ruminants) Cholestasis (early) Consider hemolysis Spherocytes Agglutination Heinz bodies RCB parasites Hemoglobinemia Hemoglobinuria Bleeding into body cavities/tissues? YES Consider increased RBC destruction NO Consider Hepatic failure Additional tests Ammonia, albumin, glucose, cholesterol Pancreatic injury (PLI) Radiology, USG Liver biopsy Abdominal fluid evaluation

42 Liver Function Tests Bile Acids Serum bile acids (SBA) are measured to evaluate hepatic function, cholestasis and portal circulatory anomalies. They are synthesized from cholesterol by hepatocytes. In most species, cholic acid and chenodeoxycholic acid are the primary bile acids. After synthesis, it is conjugated with amino acids (taurine [primary] or glycine) and released into bile. Bile acids are stored in the gall bladder. After ingestion of foods, it released to small intestine. Bile acids emulsify fat and, therefore, promote both the digestion and absorption of fat as well as of fat-soluble vitamins. Most bile acids are reabsorbed from the ileum into the portal circulation and passes through the liver and arerecirculated. In a normal physiology, only a small increase in post-prandial bile acids can be seen in serum.

43 Three main pathologic processes result in increased serum bile acids concentration. 1. Abnormalities of Portal circulation Congenital portosystemic shunts, hepatoportal microvascular dysplasia, acquired shunts due to severe cirrhosis 2. Decreased functional hepatic mass Major factor in many difduse liver diseases (hepatitis, necrosis, glucocorticoid hepatopathy) 3. Decreased bile acid excretion in bile Cholestasis deu to obstruction, hepatocyte swelling, neoplasia, inflammation

44 Liver Function Tests Serum bile acids can be used as a sensitive cholestatic indicator in suspected cases of liver disease, for example, when hepatic enzyme activity is elevated in the serum but total bilirubin is normal. It increases in cholestatic situations. Bilirubin and bile acids do not compete for hepatocytes. Therefore, it can be used in the differential diagnosis of hemolytic hyperbilirubinemia. In this case, serum bile acids do not increase. In contrast, severe anemia causes hepatocellular hypoxia and may increase the concentration of serum bile acids by causing hepatic dysfunction.

45 Liver Function Tests Bile acids are stable in serum at room temperature for several days, and serum for bile acid assays can be frozen. In dogs and cats, both fasting (pre-prandial) and postprandial samples are recommended for bile acid assays in order to provide the most reliable interpretation. For this, 1.The first sample is collected after 12 hour fasting (Pre-). 2.An appropriate volume of fat-containing formula is given to induce cholecystokinin. Thus, gall bladder contraction is stimulated. Growth diets with higher fat content are recommended. 3.The second sample is collected at 2 hours after feeding (Post-). 4.The concentration of bile acids in both samples is assessed by measuring the concentration.

46 Liver Function Tests Fasting levels of >20 μmol/l and postprandial levels of >25 μmol/l indicate liver disease in dogs and cats. In cats and dogs, fasting level of <5 μmol/l is considered normal. 5 to 20 μmol/l may indicate liver disease. On the other hand, hunger levels in normal animals are sometimes as high as 20 μmol/l. This should be evaluated together with the history of the animal, clinical findings and other laboratory tests.

47 Liver Function Tests In dogs, increased serum concentrations of bile acids may occur due to various liver diseases. These include portosystemic shunt, cirrhosis, cholestasis, necrosis, hepatitis, hepatic lipidosis, and neoplasms. Significant and exaggerated increases are observed, especially in animals with portosystemic shunt. However, it is not possible to identify the type of liver disease alone based on bile acid concentration. Abnormal bile acid concentration is a display for further testing (eg, liver biopsy, radiological examinations, ultrasonography) aimed at identifying the type of specific liver disease present.

48 Liver Function Tests In cats, elevated serum concentrations of bile acids may occur due to portosystemic shunts, cirrhosis, cholestasis, necrosis, hepatitis, hepatic lipidosis, and neoplasia. In these cats, fasting bile acid concentration is less consistently increased than postprandial concentration and it is necessary to measure both. Postprandial bile acid concentration is sometimes lower in dogs and cats than fasting bile acid concentration. This can occur due to spontaneous emptying of the gall bladder during the fasting period or to differences in gastrointestinal variables (gastric emptying time, intestinal transit, intestinal flora) or cholecystokinin secretion.

49 Liver Function Tests In horses and ruminants, a single sample is usually collected for a bile acid assay. Horses continuously secrete bile into the intestinal tract because of their lack of a gallbladder and apparent weakness of the sphincter of the common bile duct. Increased SBA concentration is a sensitive indicator of hepatobiliary disease in horses with a variety of disorders including hepatic necrosis, hepatic lipidosis, neoplasia, and cirrhosis.

50 Liver Function Tests In healthy animals only small amounts of bile acids pass through the systemic circulation and are excreted in the urine. However, when the concentration of serum bile acids increases, more bile acids are excreted in urine. Theoretically, a one-time measurement of urine bile acid concentration compared to the concentration of urine creatinine can provide similar information compared to fasting and postprandial blood samples. Urine Bile Acids:Urine Creatine Ratio (U-BA:U-Crea) However, in order to be able to make such an assessment, further studies are required.

51 Liver Function Tests Ammonia Predominantly ammonium (NH 4+ ). It is removed from portal circulation by liver. It is used in urea and protein synthesis. Due to changes in blood flow to the liver or markedly reduced number of functional hepatocytes may result in an increase in blood ammonia concentration. It is an important test for liver function. Depending on cholestasis, blood levels are not affected. Increased levels are evidence for hepatic encephalopathy.

52 Liver Function Tests Blood levels increase in animals with portosystemic shunt. Blood levels increase due to loss of 60% of hepatic functional mass. In ammonia increase, ammonia urate crystals are seen in urine. It also increases in Urea toxicity in cattles Heavy exercise in horses and dogss Horses with intestinal diseases.

53 Various forms of ammonium biurate in urine from a cat with a portosystemic shunt Kaynak: eclinpath

54 Liver Function Tests Ammonia concentration is typically measured in plasma using an enzymatic methods. It is very unstable. To collect sample, 1. Monogastric animals are fasted at least 8 hour before sampling. 2. Blood is collected and placed into EDTA or ammoniafree heparin anticoagulant, placed in an ice bath, and the plasma separated immediately (within 10 minutes). 3. Plasma is refrigerated (4 C) and assayed within minutes. Stable at - 20 C for 7 days. It should also be applied dynamic test to increase sensitivity.

55 Liver Function Tests Oral ammonia tolerance test Ammonium chloride (20 mg/ml) is used. It should never be performed in animals with fasting hyperammonemia. May cause acute ammonia toxicity. Other tests and fasting ammonia levels may be of use if uncertainty exists in a suspicious situation. 1. Fasting sample is collected. 2. Ammonium chloride (20 mg/ml) is administrated at a dose of 100 mg/kg (Total dose should not exceed 3 g). 3. The postadministration sample is collected after 30 minutes.

56 Liver Function Tests In a normal animal, the post sample increases up to fold. More (3-10 fold) are pathologic (portosystemic shunt or hepatic failure). In dogs, pet food can be used instead of ammonium chloride; Postprandial ammonia tolerance test. The blood sample is collected 6 hours after feeding. Dogs have a sensitivity of 91% for the detection of portosystemic shunts. However, it is not useful for detecting other liver diseases.

57 Liver Function Tests Albumin Liver is the site of all albumin synthesis. In cases where 60-80% of the hepatic function is not lost, hypoalbuminemia usually is not noted. Hypoalbuminemia is common in dogs with chronic liver disease (>60%). However, not common in horses with chronic liver disease (~20%). The concentration of blood albumin is affected by many nonhepatic causes. Glomerulopathy leading to loss of albumin, advanced intestinal inflammation or intestinal lymphangiectasia (protein-loss enteropathy-common in dogs). In chronic hepatopathy, the levels of IgM, IgG and IgA increase, globulin levels increase, albumin decreases and A:G ratio decreases.

58 Liver Function Tests Globulins The synthesis site of many globulins is the liver (except immunoglobulins). Hepatic failure can result in decreased synthesis. Globulin concentration usually does not decrease as much as the albumin concentration. In many cases, globulin concentration may increase with chronic liver disease, either as a result of increased acute phase protein production or immunoglobulin production (horses %50). Glucose The liver plays a key role in glucose metabolism. It is the center for glycogen metabolism and gluconeogenesis. In animals with hepatic failure, glucose concentration can vary from decreased to increased. The liver has tremendous reserve capacity for maintaining normal blood glucose levels; 70% hepatectomy does not result in hypoglycemia.

59 Liver Function Tests Urea Urea is synthesized by hepatocytes from ammonia. In animals with liver failure, the decrease in functional hepatic mass results in decreased conversion of ammonia to urea. Consequently, the blood ammonia concentration increases, and the blood urea (also known as BUN) concentration decreases. However, blood urea concentration also may decrease because of numerous other disorders.

60 Liver Function Tests Cholesterol Cholesterol is excreted in bile, so hypercholesterolemia can occur in situations that prevent bile excretion. Depending on many non-hepatic malignancies, an increase may also be seen. Cholesterol is synthesized in the liver, and blood levels may be reduced (due to lack of synthesis) in severe hepatic failure: Hypocholesterolemia. In this case, it can be used for differential diagnosis. Hypocholesterolemia is seen in dogs and cats with portosystemic shunt at 60-70%. However, many animal with hepatic failure have normal serum levels.

61 Liver Function Tests Coagulation Factors The liver plays a central role in the regulation of coagulation cascade. Many coagulation factors and anticoagulants are synthesized in the liver (such as antithrombin, protein c, protein s). In addition, there is a decrease in phylloquinone absorption due to cholestasis, which negatively affects factors II, VII, IX and X. In animals with liver disease, PT, APTT, Antithrombin activity, protein C activity and fibrinogen concentration may have abnormal. Thrombocytopenia can be seen. It should be evaluated for non-liver causes (e.g. for DIC).

62 Some laboratory findings for various liver diseases 1 Disorder ALT, AST ALP, GGT Bilirubin Bile Acids Other Functions Tests Miscellaneous Congenital portosystemic shunt N/+ ALP: N/+ (due to BALP in young animals) N Fasting: N/+ Postprandial: ++/+++ Ammonia: N/++ Albumin: N/- BUN: N/- Glucose: N/- Cholesterol: N/- PT: N/prolonged RBC microcytesis (60-70% of dogs) Ammonium biurate crystalluria Hepatic lipidosis (diffuse, cats) N/+++ ALP: N/+++ GGT: N/+ Bilirubin: N/+++ Fasting: N/+++ Postprandial: +/+++ PT, APTT: N/prolonged BUN: N/- RBC Poikilocytosis Steroid hepatopathy (dogs) N/++ +/+++ N/+ Fasting: N/+ Postprandial: N/+ N Bile duct obstruction, cholangiohepatitis, cholangitis +/++ ALP: +/+++ GGT: N/+++ N/+++ Fasting: N/+++ Postprandial: +/+++ PT and APTT prolonged if Vitamin K deficient Chronic liver disease or diffuse neoplasia N/++ N/+++ N/++ Fasting: N/+++ Postprandial: +/+++ Variable N: Normal +: High -: Low Source: Thrall et al., 2012

63 Some laboratory findings for various liver diseases - 2 Disorder ALT, AST ALP, GGT Bilirubin Bile Acids Other Function Tests Necrosis (Focal to Multifocal) Necrosis (Diffuse, or infiltrative disease) Hypoxia or mild toxic insult Focal abscesses, infarcts, neoplasms N/++ N N N N ++/++ N/++ N/++ Fasting: N/++ Postprandial: N/++ +/++ N/+ N Fasting: N/+ Postprandia: N/+ N/+ N/++ N/+ Fasting: N/+ Postprandia: N/+ Variable N N End-stage liver (Liver failure) N/++ N/+++ ++/+++ Fasting: N/+++ Postprandia: N/+++ Ammonia: N/+ Albumin: N/- BUN: N/- Glucose: N/- Cholesterol: N/- PT, APTT: Prolonged N: Normal +: High -: Low Source: Thrall et al., 2012

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65 References eclinpath. İnternet Erişim: Karagül H, Altıntaş A, Fidancı UR, Sel T, Klinik Biyokimya. Medisan, Ankara Kaneko JJ, Harvey JW, Bruss ML, Clinical Biochemistry of Domestic Animals, 6th edi. Academic Press-Elsevier Thrall MA, Weiser G, Allison RW, Campbell TW, Veterinary Hematology and Clinical Biochemistry, 2nd edi. Wiley-Blackwell

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