blood tests - gut and liver

Question 1

what are the 3 factors that serum activates of ALT and AST are based on?

Answer 1

• the extent of the damage to the tissue releasing transaminases
• the amount of each transaminase in that tissue
• the rate of clearance of the enzyme from the circulation

Question 2

what is the half life of ALT?

Answer 2

47 hours

Question 3

what is the half life of AST?

Answer 3

17 hours

Question 4

what are the biological variables to take into account with interpreting transaminases?

Answer 4

• diurnal variation
• dietary factors
• race: higher values in Africans and Hispanics
• weight

Question 5

what are the key characteristics of alkaline phosphatase (ALP)?

Answer 5

• catalyses the hydrolysis of phosphate monoesters
• membrane bound and mainly found in liver and bone
• in liver it is found in cells which are next to the canaliculi
• unregulated in response to bile obstruction and infiltrative or space-occupying lesions within the liver

Question 6

where is GGT mainly found?

Answer 6

hepatobiliary system

Question 7

GGT increases in blood concentration due to increased synthesis of what?

Answer 7

• alcohol or drugs
• biliary obstruction
• liver tumours
• smaller increase seen in hepatitis

Question 8

what are the 2 routine tests for protein synthesis?

Answer 8

• serum albumin concentration

- prothrombin time: INR

Question 9

what is the key role of the liver?

Answer 9

removal of potentially toxic substances:

• drugs
• bilirubin: end product of haem degradation

Question 10

how is bilirubin produced from haem?

Answer 10

• haem oxygenase releases the iron from the haem molecule to form biliverdin
• biliverdin is then converted to bilirubin by biliverdin reductase
• bilirubin released is tightly bound to albumin

Question 11

what is the equation for total bilirubin?

Answer 11

conjugated + unconjugated

Question 12

what are the key characteristics of conjugated bilirubin?

Answer 12

• approx 40% of total
• water soluble
• excreted in bile
• if elevated it appears in the urine giving it a dark colour

Question 13

what are the key characteristics of unconjugated bilirubin?

Answer 13

• not water soluble

- bound to albumin and does not therefore appear in the urine

Question 14

what are the 4 main presenting features of liver disease?

Answer 14

• jaundice: with or without itching
• pain: constant or colicky
• non-specific: nausea, fatigue, weight loss
• incidental laboratory finding

Question 15

what are the extrahepatic causes leading to jaundice?

Answer 15

• gallstones
• malignancy: bile duct, pancreas
• pancreatitis

Question 16

what are the intrahepatic causes leading to jaundice?

Answer 16

• hepatocellular disease
• drug induced cholestasis
• cholangitits
• cirrhosis

Question 17

what are the infections that cause hepatocellular disease?

Answer 17

• viral: hepatitis A, B, C, D, E, CMV
• parasitic: malaria
• bacterial

Question 18

what are the metabolic causes of hepatocellular disease?

Answer 18

• alcohol
• drugs
• NAFLD

Question 19

what are the autoimmune causes of hepatocellular disease?

Answer 19

• primary biliary cholangitis

- primary sclerosing cholangitis

Question 20

what are the genetic causes of hepatocellular disease?

Answer 20

• A1AT deficiency
• haemochromatosis
• Wilson’s disease

Question 21

what are the risk factors for NAFDL?

Answer 21

• age
• males > females
• metabolic syndrome
• ethnic: high in Hispanic
• diet
• sleep apnoea
• genetic

Question 22

what are the causes of unconjugated hyperbilirubinaemia?

Answer 22

• increased bilirubin production: haemolysis, resolution large haematoma
• impaired bilirubin conjugation: physiological in new born, hereditary defects of conjugation, drugs inhibiting conjugation
• impaired bilirubin uptake: poor liver perfusion, drugs