Diagnosis of disorders of the gut and liver using blood tests

Question 1

What enzymes catalyse these reactions?

Answer 1

Transaminase enzymes – ALT and AST

Question 2

Where are these enzymes found?

Answer 2

Question 3

What is the LFT?

Answer 3

Question 4

Serum activities of ALT and AST are based on which three factors?

Answer 4

• 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 5

The published half-life for ALT is ____h and for AST only ___h

Answer 5

The published half-life for ALT is 47h and for AST only 17h

Question 6

What are the 2 types of AST in hepatocytes?

Answer 6

Complicating factor – Hepatocytes have two forms of AST – cytosol and mitochondrial.

Question 7

Does BMI cause ALT to increase or decrease?

Answer 7

Increase

Question 8

What can change transaminases results?

Answer 8

1. Biological variables
   - Diurnal variation
   - Dietary factors eg coffee
   - Race - values higher if African or Hispanic
   - Weight
2. Reference range selection
   - Population exclusion criteria - the more rigorous the lower the reference range
   - Skewed distribution curve

3.Drugs - both prescribed and over-the-counter

Question 9

What is ALP?

Answer 9

Alkaline phosphatase (ALP)
catalyzes the hydrolysis of phosphate monoesters.
membrane-bound and mainly found in the liver and bone.
In liver its found in cells which are next to the canaliculi
Upregulated (rather than released due to damage) in response to bile duct obstruction and infiltrative or space-occupying lesions within the liver.

Question 10

What is GGT?

Answer 10

GGT
mainly found in hepatobillary system
Increase in blood concentration due to induction/increase synthesis:
by alcohol or drugs (anticonvulsants)
biliary obstruction
liver tumours
smaller increase seen in hepatitis

Question 11

Which tissues contain these enzymes?

Answer 11

Question 12

Both ____ and ____ may be induced by drugs or alcohol

Also some tumours contain ______

________ sometimes required

Answer 12

NB – Both ALP and GGT may be induced by drugs or alcohol

Also some tumours contain placental ALP

ALP isoenzyme pattern sometimes required

Question 13

What are Protein Synthesis routine tests and what do they test?

Answer 13

Protein Synthesis routine tests are:

• Serum albumin concentration
• Prothrombin time – INR
• Removal of potentially toxic substances:
• Drugs eg alcohol, paracetamol
• Bilirubin – end product of haem (from Hb) degradation

Question 14

How is bilirubin produced from haem?

Answer 14

80% of bilirubin is from red cells taken up by the reticuloendothelial system for degradation.

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 15

What does total bilirubin measure?

Answer 15

Total bilirubin = conjugated + unconjugated

Question 16

What is the difference between conjugated and unconjuagetd bilirubin?

Answer 16

•Conjugated

oApprox 40% of total

oWater soluble

oExcreted in bile

oIf elevated it appears in the urine giving a dark colour

•Unconjugated

oNot water soluble

oBound to albumin and does not therefore appear in the urine

Question 17

What are the presenting features of liver disease?

Answer 17

• Jaundice with or without itching
• Pain - constant or colicky
• Non-specific - nausea, fatigue, weight loss
• Incidental laboratory finding

Question 18

When is jaundice clinically identifiable?

Answer 18

Jaundice is clinically detectable at a serum bilirubin concentration of about 50 mmol/l and obvious to the individual at 100 mmol/l

Question 19

How is liver disease diagnosed?

Answer 19

• The clinical presentation
• The pattern of routine liver tests
• How these point to more specific tests including diagnostic radiology

Question 20

Female 49y colicky abdominal pain, RUQ tenderness, later jaundice, pale stools

Answer 20

• Presentation related to her pain
• Early elevation of ALP and GGT – before jaundice
• Then elevated bilirubin – recognising her jaundice
• ALT remaining relatively normal
• Pattern of dark urine and pale stools

The rise in ALP and GGT is due to enzyme induction secondary to obstruction of the biliary tree.

Question 21

What pattern of LFTs do not occur in the presence of protein synthesis inhibitors?

Answer 21

The rise in ALP and GGT is due to enzyme induction secondary to obstruction of the biliary tree.

Animal studies show this rise in serum ALP and GGT activities does not occur in the presence of inhibitors of protein synthesis.

Question 22

What are the extrahepatic and intrahepatic causes of obstructive jaundice?

Answer 22

Extrahepatic

• Gallstones – by far the commonest cause
• Malignancy – bile duct, pancreas
• Pancreatitis

Intrahepatic

• Hepatocellular disease (eg, resolving viral hepatitis)
• Drug-induced cholestasis
• Cholangitis
• Cirrhosis

Question 23

Answer 23

• Clinically generally unwell and no significant pain
• Very raised ALT with raised bilirubin
• Some elevation of ALP and GGT due to swelling of liver tissue causing mild obstruction within the liver.

However these results just show severe hepatocyte damage and not the cause of that damage – that requires additional tests – in this case virology tests showed hepatitis B as the cause.

Question 24

What does alcoholism do to AST and ALT?

Answer 24

In alcoholic hepatitis the serum activities of these transaminases are much less marked.

However the ratio of AST:ALT is frequently >2

Studies have indicated that in chronic alcohol excess mitochondrial AST is also elevated – NB its much longer half-life

Question 25

Answer 25

Clinically - Presence of itching - due to the accumulation of bile salts Laboratory * Raised serum bilirubin concentration * Obstructive pattern of liver enzymes * Raised serum IgM concentration * Raised serum cholesterol concentration * Prolonged INR * Anti-mitochondrial antibody positive

Question 26

What is a FIB 4 test?

Answer 26

\<1.45 strong predictive value for absence of fibrosis; \>3.25 strong predictive value for advanced fibrosis

Question 27

Whats the diagnosis? * Serum bilirubin within the reference interval * Slightly raised transaminase activities * Rather greater increase in ALP and GGT activities * Slightly low albumin and raised globulin concentrations * Mild anaemia with macrocytosis but no decrease in B12 or folate * Rather low platelet count * Slightly raised serum ferritin concentration * Mild hypocalcaemia with low serum 25-OH Vit D concentration * Borderline high serum AFP concentration * High FIB-4 score

Answer 27

Mild hypocalcaemia with low serum 25-OH Vit D concentration – this would trigger a parathyroid hormone response and ALP activation from bone Borderline high serum AFP concentration – marker for hepatocellular carcinoma High FIB-4 score indicating probable cirrhosis

Question 28

What are the markers of liver fibrosis?

Answer 28

* The FIB-4 score is derived from the formula: * NFS is derived from the formula: * The Enhanced Liver Function test (ELF) - combines three serum markers measured by immunoassay; hyaluronic acid (HA), procollagen III amino terminal peptide (PIIINP) and tissue inhibitor of metalloproteinase 1 (TIMP-1) using an algorithm developed by the European Liver Fibrosis Group.

Question 29

What are the causes of hepatocellular disease? Infections - Metabolic - Autoimmune - Genetic -

Answer 29

Infections * Viral - Hepatitis A,B,C,D,E, CMV * Parasitic – malaria * Bacterial Metabolic * Alcohol * Drugs – paracetamol poisoning * NAFLD Autoimmune * Primary biliary cholangitis * Primary sclerosing cholangitis Genetic * A1AT deficiency * Haemochromatosis Wilson’s disease

Question 30

Label each diagnosis

Answer 30

Question 31

What investigations would be done for persistently elevated serum ALT activity?

Answer 31

* LFTs inc GGT and AST * Total protein, albumin, immunoglobulins * Glucose, lipids – Metabolic syndrome, NAFLD * Full blood count - MCV * Autoimmune profile * Iron, transferrin, saturation, ferritin * Copper, caeruloplasmin, a1 antitrypsin, coeliac screen * Viral studies – Hepatitis, CMV, HIV * Carbohydrate deficient transferrin * Drug history is also important

Question 32

Answer 32

Serum bilirubin within its reference interval Mixed pattern of liver enzymes Very elevated serum iron concentration with a high saturation of transferrin Very elevated serum ferritin concentration Elevated HbA1c These are the findings in haemochromatosis: Genetic screening for those of N European ancestry is for C282Y/H63D mutations. If positive family studies are indicated. Treatment by venesection

Question 33

Answer 33

* Very Obese * Borderline fasting hyperglycaemia * Serum bilirubin within the reference interval * Elevated serum ALT and AST activities * ALT\>AST * Serum ALP activity within the reference interval for a growing child * Elevated serum triglyceride and cholesterol concentrations Other metabolic causes of liver disease excluded Probable diagnosis Non-alcoholic Fatty Liver Disease - NAFLD

Question 34

What is non-alcoholic fatty liver disease?

Answer 34

NAFLD is present when \>5% of hepatocytes are steatotic in patients who do not consume excessive alcohol.

Question 35

What are the risk factors for NAFLD?

Answer 35

* Age * Males \> Females * Metabolic syndrome * Ethnic – high in Hispanic * Diet – saturated fat, high fructose * Sleep apnoea * Genetic

Question 36

What are the 3 stages of NAFLD?

Answer 36

* 90% simple steatosis – reversible and relatively benign * Of these 10-30% progress to NASH – non-alcoholic steatohepatitis * Of these 25-40% develop fibrosis - cirrhosis

Question 37

When can you find incidentally abnormal LFTs?

Answer 37

* ~ 5% population * Transient impossible to explain * Obesity – metabolic syndrome * Medication * Non-Alcoholic Fatty Liver Disease (NAFLD) 26% * Alcohol related liver disease (ARLD) 25% * Hepatitis B/C, haemochromatosis, autoimmune \< 1% each

Question 38

Whats the diagnosis? Unconjugated hyperbilirubinaemia Normal haematology Serum haptoglobin within its reference interval

Answer 38

Gilbert’s syndrome is relatively common – perhaps 3-7% of the population. The serum bilirubin concentration is usually 20 - 40 umol/L and rarely reaches 80 umol/L.

Question 39

What are the causes of unconjugated hyperbilirubinaemia?

Answer 39

•Increased bilirubin production oHaemolysis oResolution large haematoma •Impaired bilirubin uptake oPoor liver perfusion oDrugs eg rifampicin •Impaired bilirubin conjugation oPhysiological in new-born – due to hepatic immaturity oHereditary defects of conjugation - UDP-glucuronosyltransferase Gilbert syndrome (mild but common) Crigler-Najjar syndrome type I and II (rare and more severe) oDrugs inhibiting conjugation - chloramphenicol, gentamycin, protease inhibitors

Question 40

What does this show?

Answer 40

Typical Blood Film – Haemolytic Anaemia This picture shows red blood cells of varying shape and colour density - the darker red cells have lost their slightly paler centre of the normal biconcave disc and are spherical; others are just very misshapen and there is a large variation in red cell size.

Question 41

How does a Direct Antiglobulin Test (Coomb’s test) work?

Answer 41

Question 42

Unconjugated hyperbilirubinaemia Elevated red cell enzyme activities – LDH\>AST\>ALT Very low serum haptoglobin concentration Very abnormal blood film Positive anti-globulin test Whats the diagnosis?

Answer 42

Autoimmune haemolytic anaemia