Biochemical Investigation of Liver Function

Question 1

What is the functional unit of the liver ? Describe the contents of this unit and structures surrounding this.

Answer 1

Liver lobule.
Each lobule hexagonal in shape and composed of: hepatocytes (parenchymal cells) arranged in plates, in contact with bloodstream on one side and bile canaliculi (“little canals”) on the other.

Between the plates are vascular spaces (sinusoids) containing Kupffer cells (phagocytic macrophages)

Question 2

Is the liver a metabolic, or excretory organ ?

Answer 2

Both a metabolic and excretory organ

Question 3

Identify the main functions of the liver.

Answer 3

• METABOLIC Functions – Carbohydrates, Hormones, Lipids, Drugs and Proteins
• STORAGE–Glycogen, vitamins, iron
• PROTECTIVE – Detoxification and elimination of toxic compounds, Kupffer cells ingest bacteria and other foreign material from blood, as well as old blood cells
• BILE production (through conjugation of bilirubin) and excretion– formed in biliary canaliculi, emulsifies fats and provides route for waste removal

Question 4

Identify the main types of liver disease.

Answer 4

• Infection – Viral (Hepatitis A-E, CMV), bacterial, parasitic
• Toxic / Drug induced
• Autoimmune
• Biliary tract obstruction – Tumours, gallstones
• Vascular
• Metabolic–haemochromatosis, Wilson’s, hereditory hyperbilirubinaemias.
• Neoplastic

Question 5

Identify the main causes of acute hepatitis.

Answer 5

• Poisoning (paracetamol)
• Infection (Hepatitis A-C)
• Inadequate perfusion

Question 6

Identify the possible outcomes of acute hepatitis.

Answer 6

• Resolution – majority of cases
• Progression to acute hepatic failure
• Progression to chronic hepatic damage

Question 7

Identify common causes of chronic liver disease.

Answer 7

• Alcoholic fatty liver
• Chronic active hepatitis
• Primary biliary cirrhosis

Question 8

Identify unusual causes of chronic liver disease.

Answer 8

• α-1 AT deficiency (does not always cause disease)
• Haemochromatosis
• Wilson’s disease (usually presents early, unlikely in a patient over 40)

Question 9

Define Cholestasis.

Answer 9

Failure to produce or excrete bile, resulting in accumulation of (conjugated) bilirubin in the blood leading to Jaundice.

Question 10

Identify any other causes of jaundice besides Cholestasis. What is the difference between the appearance of bilirubin in jaundice due to Cholestasis, and jaundice due to excessive haemolysis.

Answer 10

Jaundice may also be due to excessive haemolysis – bilirubin is unconjugated and does not appear in the urine (whereas when it is due to Cholestasis, bilirubin is conjugated.

Question 11

Identify the main consequences of liver failure.

Answer 11

• Inadequate synthesis of albumin leading to oedema and ascites
• Inadequate synthesis of clotting factors resulting in bruising
• Inability to eliminate bilirubin causing jaundice
• Inability to eliminate nitrogenous waste e.g. ammonia, giving rise to hepatic encephalopathy, a poorly defined neuro- psychiatric disorder.

Question 12

What questions are we attempting to answer through an investigation of liver disease ?

Answer 12

• Is liver disease present?
• What is the aetiology?
• What is the severity?

Question 13

Identify the main current liver function tests (LFT). What/which condition does each test for ?

Answer 13

• Albumin: for synthetic function (if low)
• ALT (and AST): Aminotransferases for hepatocellular damage (if raised)
• ALP (γ-GT): for biliary epithelial damage and obstruction (if raised)
• Bilirubin: for cholestasis (bile flow blockage)

Question 14

Identify the main pros, and cons of the current LFTs.

Answer 14

PROS:

• cheap, widely available, interpretable
• direct subsequent investigation (e.g. imaging)

CONS:
– Do not assess liver “function”
– Lack of complete organ specificity
– Lack of disease specificity
– May be “over-sensitive” (suggest disease when nothing)
– >40 years old, many newly discovered diseases for which they have no diagnostic value
– LFT’s may be only subtly altered
– Often not followed up or simply repeated multiple times

Question 15

What is the significance of albumin ?

Answer 15

Main plasma protein

Question 16

Low albumin may indicate poor liver synthetic function. What other conditions/situations may low albumin be found in ?

Answer 16

– Post-surgical/ITU patients due to redistribution
– Significant malnutrition
– Nephrotic syndrome (losing all the proteins in the kidney, nothing wrong with kidney)

Question 17

Define ALT and AST. Why are they used as liver function tests ? Where else in the body may they be found ?

Answer 17

Alanine Aminotransferase, and Aspartate Aminotransferase.

Because they are sensitive, non specific markers of acute damage to hepatocytes.
→ Cytoplasmic enzymes also found in cardiac muscle and erythrocytes.

Question 18

Define ALP. Why are they used as liver function tests ? Where else in the body may they be found ?

Answer 18

Alkaline phosphatase.
Increased in liver disease due to increased synthesis in response to cholestasis
→ also present in bone, gut and placenta

Question 19

Identify the main liver enzymes which are significant for investigations.

Answer 19

ALT and AST
ALP
γ-GT

Question 20

Why is γ-GT used as liver function tests ? Where else in the body may they be found ?

Answer 20

γ-GT – (non-specific but very sensitive) raised in cholestasis, also affected by ingestion of alcohol and drugs such as phenytoin

→ also present in bone, biliary tract, pancreas and kidney.

Question 21

What is bilirubin ?

Answer 21

Breakdown product of haemoglobin

Question 22

Describe the process of bilirubin processing.

Answer 22

-Unconjugated bilirubin taken up by liver and
conjugated

• Conjugated bilirubin excreted in bile
• Attacked by bacteria in colon and excreted in faeces
• Small amounts reabsorbed and excreted in urine as urobilinogen

Question 23

Identify the main possible causes of Cholestasis. What is the net result of cholestasis ?

Answer 23

1) Failure by hepatocytes – “intrahepatic cholestasis”
2) Obstruction to bile flow –”extrahepatic obstruction” (causing back pressure onto liver, possibly causing liver)

Can also be combination of both

Net result, accumulation of bilirubin in circulation and jaundice

Question 24

Describe possible causes of abnormal LFTs in a patient whose liver has no problem.

Answer 24

• Bilirubin (raised)
-haemolysis, Gilberts syndrome

• ALP (raised)

• Pathology of bone, placenta, gut
• Physiological e.g., pregnancy, childhood

• ALT (raised)
-Skeletal muscle disorders, MI

• γ-GT (raised)
-alcohol, drugs

Question 25

What are possible aetiologies of liver disease ? Which investigations are used for these ?

Answer 25

* Hepatitis serology * α-1 antitrypsin deficiency * α-fetoprotein – tumour marker (hepatocellular carcinoma) (fetal form of albumin, then declines and albumin takes over) * Caeruloplasmin/copper studies (both)– Wilson’s disease * Iron studies-Haemochromatosis * Autoantibodies – chronic active hepatitis, PBC (primary biliary cholangitis) * Radiology–obstruction, hepatomegaly * Liver biopsy

Question 26

How can we establish the severity of liver disease, based on LFTs ?

Answer 26

• Pattern recognition is important. – LFT’s may be normally or mildly increased in patients with chronic disease e.g. cirrhosis (because not very much liver left) – Small changes may be significant (e.g. decompensation, long-standing chronic disease) – Some quite marked increases may be of no apparent consequence. – Long term consequences may be as yet unknown.

Question 27

How prevalent is liver disease ? Is this likely to further increase (why/why not) ?

Answer 27

• Liver disease is on the increase: – 3rd most common cause of death in men < 65 years – Likely to rise further due to alcohol consumption and obesity

Question 28

How early is liver disease usually identified ? How does this affect mortality ? How does this affect costs to the NHS ?

Answer 28

Liver disease is often identified late: – Increased mortality – Increased costs to the NHS

Question 29

What is the problem with current LFTs ?

Answer 29

* LFT’s may be only subtly altered | * Often not followed up or simply repeated multiple times

Question 30

Which patients are intelligent LFTs used for ?

Answer 30

Patients with abnormal LFT’s in whom the cause is unclear: | – Patients with frank jaundice excluded.

Question 31

What do intelligent LFTs consist of ?

Answer 31

A combination of biochemistry, haematology and serology in conjunction with liver ultrasound.

Question 32

What are the main steps of the process of doing iLFTs (intelligent LFTs)?

Answer 32

1) Patient specific data: Age, gender, BMI, features of metabolic syndrome (diabetes, high BP), alcohol intake. 2) LFT and FBC performed: ALT, albumin, bilirubin, alk phos, γGT and platelets. ------- → ALT, Alk phos and γGT all normal: No further tests. → Any of ALT, Alk phos and γGT abnormal: – Aetiology screen: Hepatitis serology, liver immunology, ferritin, alpha- 1 antitrypsin, caeruloplasmin, AST, γGT, platelet count and – Fibrosis staging - FIB4 score (Age, AST, ALT and platelet count) - NAFLD fibrosis score (Age, BMI, impaired fasting glucose /frank diabetes, AST, ALT, Albumin, platelets)

Question 33

Identify the possible diagnoses of a patient with hyperbilirubinaemia, following the different investigation results which may arise.

Answer 33

FIRST STEP: ALP AND ALT 1) Normal → look at conjugated bilirubin -If normal amount of conjugated bilirubin ((~<20% of total), then maybe haemolysis, Gilbert's syndrome, or Crigler-Najjar Dubin Johnson's syndrome. -If increased levels of conjugated bilirubin, then Dubin Johnson syndrome, or Rotor syndrome 2) Increased ALT/ALP → look at ALT specifically - If ALT is normal, but ALP is increased, it's predominantly Cholectasis - If ALT is increased by less than 10 fold, and ALP is increased by more than 3 fold, then it's predominantly Cholectasis - If ALT is increased by less than 10 fold, and ALP is increased by less than 3 fold, then Cholectasis and/or hepatocellular - If ALT is increased by more than 10 fold, and ALP is increased by more than 3 fold, then Cholectasis and/or hepatocellular. - If ALT is increased by more than 10 fold, and ALP is increased by less than 3 fold, it's predominantly hepatocellular

Question 34

Summarise the findings of LFTs for acute hepatocellular damage.

Answer 34

Bilirubin: very raised ALT: very raised Alk Phos: normal or a bit raised Gamma GT: normal or a bit raised

Question 35

Summarise the findings of LFTs for chronic hepatocellular damage.

Answer 35

Bilirubin: normal or a bit raised ALT: normal or a bit raised Alk Phos: normal or a bit raised Gamma GT: normal or a bit raised

Question 36

Summarise the findings of LFTs for cholestasis.

Answer 36

Bilirubin: very raised ALT: a bit raised Alk Phos: very raised Gamma GT: very raised

Question 37

Explain the process of patient stratification when a patient comes in with raised ALT, Alk phos or Gamma GT.

Answer 37

1) Initial raised ALT, ALP, or Gamma GT - If Bilirubin > 22 umol/L → Jaundice investigation ------- -If Bilirubin < 22 umol/L → α1AT, AST, Iron studies, Caer (<35 y), Hep B, Hep C and Fibrosis scoring ↓ -If no abnormality identified, Further immunology tests/US ↓ -if findings are ``` 1) •Autoimmune disease •NAFLD/ARFLD with indeterminate or raised fibrosis score or •abnormal immunology, then ↓ Refer to hepatology ``` 2) NAFLD/ARFLD with low fibrosis score ↓ GP review (subject to results of US) 3) Other ↓ GP review (subject to results of US) -------- ``` -If Bilirubin < 22 umol/L → α1AT, AST, Iron studies, Caer (<35 y), Hep B, Hep C and Fibrosis scoring ↓ If abnormality identified: •Hep B or C •Specific protein abnormality • Abnormal iron studies ↓ Refer to hepatology ```

Question 38

Identify the main clinical features of Gilbert’s syndrome.

Answer 38

* Auto-immune * Fluctuating hyperbilirubinaemia * Characterised by intermittent mild jaundice evident during periods of fasting and illness * Due to conjugating defect in liver * Benign and no treatment required

Question 39

What are possible consequences of alcohol on the liver ?

Answer 39

Can also result in an isolated elevation of γGT, or also hepatocellular damage, possibly resulting in fatty infiltration, alcoholic hepatitis or cirrhosis