Lab Investigation of Liver & GI Tract Disease Flashcards
Describe the size of the liver
The liver is the largest organ in the body, 1.5 kg in an average 70 kg male situated in upper right quadrant
How many lobes is the liver comprised of?
Comprised of large right lobe and smaller left lobe composed of lobules
What are lobules?
Lobules - sheets of hepatocytes
Describe the blood supply to the liver
Has dual blood supply
2/3 from gut via portal vein (nutrient rich)
1/3 from hepatic artery (oxygen rich)
How does blood drain from the liver?
Blood leaves the liver through the hepatic veins
Where are liver excretions removed from?
Substances for excretion from the liver are secreted from hepatocytes into canaliculi
Describe how the liver connects to the bile duct
The bile canaliculi merge and form bile ductules
They subsequently merge to become a bile duct; eventually common hepatic duct.
What are the major functions of the liver?
- Carbohydrate metabolism (gluconeogenesis)
- Fat metabolism
- Protein metabolism of plasma proteins
- Hormone metabolism (peptide and steroid hormones)
- Metabolism + excretion of drugs / foreign compounds
- Storage: glycogen, vitamin A, B12, iron and copper
- Metabolism and excretion of bilirubin
What is hepatitis?
Damage to hepatocytes
What is cholestasis?
Blockage; Intra or extrahepatic (e.g. bile ducts)
Outline the damage caused to the liver in cirrhosis
- Increased fibrosis
- Liver shrinkage
- Decreased hepatocellular function
- Obstruction of bile flow
What are the different tumours of the liver?
Primary cancer
Frequently secondary: colon, stomach, bronchus
How do we assess liver function?
Liver Function Test (LFT) provides a biochemical assessment of liver function
What markers are measured in a standard LFT?
- Bilirubin
- Albumin
- Alanine aminotransferase (ALT)
- Aspartate aminotransferase (AST)
- Alkaline phosphatase
- Gamma glutamyltransferase (gamma GT)
What does an LFT show us?
Insensitive indicators of liver ‘function’
Look for patterns of results - a single result rarely provides a diagnosis on its own
What is a LFT used for?
Not diagnostic but used for:
- Screening for liver disease
- Assessing prognosis
- Differential diagnosis; hepatic / cholestatic?
- monitoring disease progression
- Treatment efficacy measurement
- Severity assessments esp. cirrhosis
When would we expect to see a decrease in albumin levels?
Albumin concentrations only tend to decrease in chronic liver disease
What is bilirubin?
Yellow-orange pigment derived from haem from Hb breakdown
What are the 2 forms of bilirubin?
- Conjugated (direct-reacting bilirubin)
- Unconjugated (indirect-reacting bilirubin) - v. hydrophobic
What is the normal range of bilirubin?
Total bilirubin – SWLP Reference range <21 μmol/L
Conjugated (direct) bilirubin <10 μmol/L
How is bilirubin found in the body?
Binds tightly but reversibly to albumin
Where does conjugation of bilirubin occur?
Conjugation occurs in the liver → excreted in bile
Where are RBCs broken down?
Old RBCs undergo haemolysis in the spleen
What happens to the breakdown products of old RBCs in the spleen?
Fe is reutilised, Globin from Hb is transferred into bilirubin
Where is bilirubin conjugated?
Bilirubin transported to liver; albumin bound where its conjugated
Outline how conjugation occurs in the liver
Bilirubin is conjugated to diglucuronide via UDP-glucuronyl transferase enzyme
What is the product of bilirubin conjugation?
Leads to conjugation of mono / diglucuronides which are more water soluble, excreted via bile ducts into small intestine
How is bilirubin excreted?
Bilirubin converted to urobilinogen in small intestine
Re enters liver via extrahepatic circulation or enters systemic circulation to be excreted via kidneys
How is bilirubin excreted in faeces?
Some urobilinogen remains and reaches large intestine where it is converted into stercobilin by colon bacteria (gives stool brown colour)
What is jaundice?
Jaundice describes the yellow discolouration of tissue due to bilirubin deposition.
Mainly in skin and visualised in sclera
When does jaundice become noticeable?
Clinical jaundice may not be evident until the serum/plasma bilirubin concentration is 2x the upper reference of normal, >50 μmol/L
What causes jaundice to occur?
Increased serum/plasma [bilirubin] occur in imbalance between production & excretion
What is the first step in treating jaundice?
Important to determine if ↑bilirubin is conjugated or unconjugated (allows identification of liver function)
What does conjugated bilirubn elevation tell us?
Conjugated bilirubin elevation – obstruction of bilirubin flow
What does excess unconjugated bilirubin jaundice mean?
Unconjugated elevation - production is increased which is beyond capacity of liver conjugation
What are the prehepatic causes of jaundice?
Excess bilirubin production due to excessive RBC breakdown e.g.
- Haemolysis
- Haemolytic anaemia
- Genetic disorders
- Crigler-najjar
- Gilberts
What is gilberts syndrome?
Benign liver disorder, diagnosed on exclusion
Congenital disorder of UDP-glucuronyl transferase
What are the main causes of intrahepatic jaundice?
Damaged hepatic cells leading to cholestasis (both conjugated and unconjugated bilirubin present)
What factors leads to dysfunction of hepatic cells?
- Viral hepatitis
- Drugs
- Alcohol hepatitis
- Cirrhosis
- Pregnancy
- Infiltration
- Congenital disorder
What is the cause of extrahepatic jaundice?
Blockage of canaliculi due to conjugated bilirubin - impaired excretion
What may cause obstruction of the biliary drainage system?
- common duct stone
- carcinoma
- biliary structure
- sclerosing cholangitis
- pancreatitis
What causes neonatal jaundice?
Due to the immaturity of bilirubin conjugation enzymes
Common & transient (resolves in the first 10 days)
What are the consequences of neonatal jaundice?
High levels of unconjugated bilirubin - toxic to newborn → due to its hydrophobicity , can cross the blood-brain-barrier & cause kernicterus
What are the effects of kernicterus?
Kernicterus causes drowsiness and hypotenosity and seizures (can cause severe brain damage)
How is neonatal jaundice resolved?
Phototherapy with UV light – converts bilirubin to water soluble, non-toxic form
What causes pathological neonatal jaundice?
Pathological jaundice if high levels of conjugated bilirubin
Can be due to inborn errors of metabolism (galactosemia / tyrosinemia affecting liver)
E.g. Pale stools in babies with biliary atresia. Urgent surgical treatment is essential.
What is the frequency of gilberts syndrome?
Frequency : 10% of population
Males more frequently affected than females
Occurs when fasting or under physiological stress
What are the characteristics of gilberts syndrome?
Characterized by mild, fluctuating increases in unconjugated bilirubin
What are the causes of gilberts syndrome?
→ caused by ↓ ability of the liver to conjugate bilirubin
- genetic defect in promoter gene for UDP glucuronyl transferase
What are the most commonly measured markers of hepatocyte injury?
Liver Transaminases ALT and AST
What is the role of liver transaminases?
Catalyse transfer of amino group into acids
α -amino acid → α-oxo acid
What is ALT?
ALT Alanine Aminotransferase (ALT): predominantly localised to liver
What is AST?
AST Aspartate Aminotransferase (AST) has wide tissue distribution: heart, skeletal muscle, kidney, brain, erythrocytes, lung & liver
Where in hepatocytes are liver transaminases found?
Both are cytosolic but AST is also present in mitochondria
What is ALT used for?
ALT is used to identify liver damage arising from hepatocyte inflammation or necrosis
What do increases in ALT levels tell us?
Values >20x the upper limit of normal (ULN) may occur with severe liver damage
Small increases (<5x ULN) may occur in cholestasis due to secondary damage to hepatocytes.
When do AST and ALT levels increase?
Values increased in almost all liver disease
Which conditions are responsible for modest elevations in ALT and AST levels?
(5 x ULN):
- Fatty liver
- Chronic viral hepatitis
- Prolonged Cholestatic liver disease
- Cirrhosis
Why may ALT/AST levels return to normal in cirrhosis?
In compensated cirrhosis values may be normal
May get decreased increase due to less liver being available as so much damage has occurred
What causes major elevations in AST/ALT levels?
Highest elevation (10-20x ULN) severe hepatocyte damage
- Acute viral hepatitis
- Hepatic necrosis induced by drugs or toxins
- Ischaemic hepatitis induced by circulatory shock
What is the role of alkaline phosphatase?
ALP removes phosphate groups from proteins and nucleic acids at alkaline pH (9-10.5)
What is ALP used as a marker for?
Good marker for cholestasis, ALP found in bile canaliculi
What marker do we expect to see in bile duct obstruction?
Bile duct obstruction - increased ALP synthesis and thus increase in measured activity
What are the causes of bile duct obstruction?
Obstruction may be due to:
Extrahepatic
- stones, tumour or stricture
Intrahepatic
- infiltration or space occupying lesion
Where is ALP formed?
Enzyme isoforms mainly produced in liver and bone but also placental and intestinal forms - not v. specific
What are the expected ALP values in varying liver diseases?
ALP values >3 x ULN
- Intra- & extrahepatic cholestasis
ALP values <3 x ULN
- Hepatocellular disease
Age and sex related reference ranges (as found in bone)
How do ALP levels change during osteoblastic activity?
↑↑ in osteoblastic activity:
- Healing fractures
- Vitamin D deficiency
- Paget’s disease
How can we identify the source of ALP elevation?
The source of an elevated ALP can be determined by gel electrophoresis
- enables separation of ALP isoenzymes into liver, bone, and intestinal fractions.
How is placental ALP identified?
The placental isoenzyme of ALP can be identified as it is heat stable at 65oC for 10 minutes, unlike the other isoenzymes.
What is GGT?
Gamma Glutamyl Transferase (GGT) is a membrane bound enzyme
What is the role of GGT?
GGT transfers the gamma glutamyl group from peptides such as glutathione to other peptides and to L-amino acids
Where is GGT localised?
Wide tissue distribution, but liver isoenzyme activity predominates in serum
What is the LFT use of GGT?
Used in combination with ALP, ↑ value confirms ALP of hepatic origin
When would we see elevated GGT results in nonhepatic disorders?
Can be ↑ in non-hepatic disorders, e.g. pancreatitis, myocardial infarction and diabetes mellitus
How do drugs and alcohol effect GGT?
↑ levels may be due to enzyme induction by alcohol or drugs e.g. anticonvulsants.
How does cholestasis effect GGT?
↑ levels occur in cholestasis and hepatocellular disease
Outline some common interpretations of GGT and ALP results?
↑ ALP and ↑ GGT
– suggestive of hepatic cause (cholestasis)
↑ ALP and N GGT
– suggestive of bone source of ALP
N ALP and ↑ GGT
– suggestive of excess alcohol intake
What is albumin?
Major circulating plasma protein
Where is albumin formed?
Synthesised exclusively in the liver, 12g produced each day - crude synthetic test
What can [albumin] tell us?
Concentration widely regarded as an index of hepatic synthetic function
Why may albumin levels be normal in hepatitis?
Can be normal in early acute hepatitis due to its long half-life (21 days)
Values may be normal in well compensated liver disease
How do liver diseases effect albumin levels?
Acute or chronic destructive liver diseases of moderate severity show decreased serum albumin
What disorders decrease albumin levels?
Decreases also consistent with:
- Haemodilution
- Impaired synthesis
e. g. malnutrition - Increased loss
e. g. nephrotic syndrome - Inflammatory leak
Outline the prevalence of Non Alcoholic Fatty Liver Disease
NAFLD more prevalent than alcoholic liver disease
Prevalence
20% in general population
Up to 70% in type 2 diabetes
What are the stages of NAFLD
Hepatic steatosis (fat >5% liver volume)
Greater risk of progressing to fibrosis, cirrhosis, HCC
What is steatosis?
Abnormal retention of fat (lipids) within a cell or organ
What are the major risk factors of NAFLD?
- Obesity
- Diabetes/insulin resistance
- Hypertension
How can we differentiate between ALD and NAFLD?
Can differentiate between NAFLD and ALD just by ALT and AST markers
Describe common differences between ALD and NAFLD
Increased AST in alcoholic diseases so AST:ALT ratio good indicator (>1.5)
Describe the prognosis for patients with unidentified cause of NAFLD
For patients with NAFLD / liver disease of unknown aetiology, the next step is to determine the likelihood of liver fibrosis
Describe the initial test carried out to identify liver fibrosis risk
Initial assessment includes calculation of FIB4 or NAFLD fibrosis score with values <1.3 and ≤1.455, respectively, signifying a low risk of advanced fibrosis
How do we assess older patients risk for liver fibrosis?
Higher cut-off points, <2.0 and <0.12, should be used for patients aged over 65 years
Outline second line tests that should be considered for diagnosing liver fibrosis
Second-line tests that should be considered include:
- serum markers (ELF)
- imaging modalities (ARFI elastography/FibroScan)
Describe the structure of the GI tract
GI tract runs from mouth → anus
What are the functions of the GI structrues?
Different structures have varying functions; the main GI function is absorption of food:
- Involves enzymes
- pH dependent
Describe the anatomy of the GI tract
- Oesophagus
- Stomach
- Small intestine
- intestine (colon)
Accessory organs:
- Liver
- Pancreas
- Gallbladder
Describe the muscle composition of the GI tract
GI tract is composed of ⅔ smooth muscle and ⅓ skeletal muscle
Describe the movement along the GI tract
Movement occurs in waves; peristalsis
Requires ~30% of Cardiac output
How is GI function mediated?
GI also has an enteric endocrine system enabling regulation of GI functions
What causes gastric ulcers to occur?
Gastric ulcers are caused by a break in the protective stomach mucosal lining or in duodenum
What are the secretions of the stomach and gut lining?
Stomach produces acid and pepsin as part of the digestive process
Mucous is also secreted to protect the stomach from the high acidic conditions
Describe the signs and symptoms of gastric ulcers
- Fluctuating abdomen pain (eased with antacid)
- Waking up due to abdomen pain
- Bloating, retching and feeling sick
- Feeling particularly ‘full’ after a normal size meal
What are the common causes of gastric ulcers?
Helicobacter pylori infection (80% of cases)
Use of aspirin and NSAIDs – non-steroidal anti-inflammatory drugs (20% of cases)
What is H. pylori?
H. pylori - helix-shaped gram-negative bacteria, survives in gastric acid by secreting urease
Also produces and releases toxins that cause further epithelial cell damage
What is the role of urease?
Urease breaks down urea to form CO₂ and ammonia (NH₃)
What is the role of Ammonia in the stomach?
NH₃ is a basic compound; helps neutralise acids in stomach
What is the urea breath test?
The urea breath test is a rapid and non-invasive procedure used to identify active infection by H. pylori.
Outline how the urea breath test is conducted
- Patient drinks urea containing solution labelled with an isotope (non-radioactive carbon-13).
- Detection of isotope-labelled carbon dioxide in exhaled breath indicates urea was split by urease-secreting H. pylori, present in stomach
What is Vit. B12?
Vitamin B12 (cobalamin) is a water soluble vitamin
Essential role in nervous system and RBC formation as a cofactor for DNA synthesis
How is Vit.B12 obtained?
Vitamin B12 cannot be produced by the human body and so must be obtained from the diet
How is B12 transported in the body?
When dietary B12 enters the stomach it is bound by intrinsic factor (IF), a 45 kDa glycoprotein by the parietal cells of the stomach
How does B12 reach its target organs?
B12-IF complex enters intestine where it binds to receptors on internal ileum mucosal cells where B12 is released
B12 absorbed into bloodstream by transcobalamin and transported to its target tissues and liver for storage
Why may B12 deficiency take a while to present itself?
The liver contains a large store of vitamin B12. May take a long period of time for vitamin B12 deficiency to present itself
Which disorder is commonly associated with B12 deficiency?
Pernicious anaemia, an autoimmune attack on the gastric mucosa, causes severe Vitamin B12 deficiency
Leads to atrophy of stomach wall and IF secretion is absent or severely depleted
Outline the function of B12 in DNA and cell formation
Important cofactor for various enzymes
e.g. aids conversion of homocysteine → methionine; essential amino acid used for DNA precursors production - cell division issues
Explain the role of B12 in the CNS
Also involved in methylmalonyl CoA → succinyl CoA (Krebs) - B12 deficiency causes build up of MCoA which impairs myelin sheath function ⇒ neuropathy - CNS issues
What are the signs and symptoms of B12 deficiency?
- Macrocytic/Megaloblastic anaemia (increased MCV, decreased haemoglobin) - Weakness and tiredness - Pale skin - Glossitis – inflammation of the tongue - Nerve problems such as numbness or tingling (severe deficiency)
Outline the deficient level of B12
Serum vitamin B12 level: <150 pmol/L indicates probably B12 deficiency
Describe how B12 deficiency effect methylmalonic acid levels
Methylmalonic acid: elevated in tissue B12 deficiency (may also be elevated in renal disease)
How do Homocysteine levels change in B12 deficiency?
Homocysteine: elevated in B12 deficiency as not converted to methionine. Less specific than MMA as it is also elevated in folate deficiency and hypothyroidism, but test is more readily available
What are the effects of B12 deficiency on holotranscobalamin?
Holotranscobalamin (active B12): measurement of B12 bound to transcobalamin and may be the first detectable marker of B12 deficiency
How does pernicious anaemia effect IF?
Intrinsic factor and antiparietal cell antibodies are positive in pernicious anaemia
What is coeliac disease?
Coeliac disease is an autoimmune disorder, primarily affecting the small intestine.
What is the physiological cause of coeliac disease?
Disease results from immunological hypersensitivity to ingested gliadin (gluten protein) in wheat and other grains such as barley and rye
Upon gluten exposure in small intestine an inflammatory reaction occurs leading to shortening of villi lining and villous atrophy
How many people suffer from coeliac?
Affects up to 1% of the general population and may present at any age
What are the classic symptoms of coeliac?
Classic symptoms of coeliac disease include anaemia, weight loss, and GI problems e.g. diarrhoea, abdominal distention, malabsorption and loss of appetite
What do we use to test for coeliac?
Tissue Transglutaminase Antibodies
What is tissue transglutaminae?
Tissue transglutaminase (TTG) - enzyme that deaminates glutamine residues to glutamic acid on gliadin fragment
Target autoantigen in immune response, leading to destruction of intestinal epithelial cells and production of anti-TTG antibodies
Describe the anti-TTG test
Anti-TTG antibodies are IgA
Approximately 1 in 700 people in UK are deficient in IgA so this test would produce a false negative result in IgA deficient patients with coeliac disease - not used for diagnosis
What alternative to anti-TTG is used to diagnose Coeliac?
IgG deamidated gliadin peptide (DGP) antibodies
What other coeliac tests are available?
Endomysial antibodies (EMA): elevated due to ongoing damage to intestine
Duodenal biopsy - gold standard
Gluten challenge: patients already on a gluten-free diet cannot be diagnosed as serology and histology tests will be normal until gluten is ingested.
What is inflammatory bowel disease?
Inflammatory bowel disease (IBD) encompasses two distinct autoimmune conditions of the GI tract: Ulcerative colitis and Crohn’s disease
What is ulcerative colitis?
Diffuse inflammation affecting the mucosa of the colon only.
What is crohns disease?
Patchy ulceration affects any part of GI tract and may extend through full thickness of bowel
Complications: fistulae, abscess formation and stricturing.
How is IBD diagnosed?
Colonoscopy is the definitive test for diagnosis of IBD
What are the signs and symptoms of IBD?
Crohn’s disease and Ulcerative colitis have common signs and symptoms:
- Abdominal pain
- Prolonged diarrhoea w/ bowel urgency
- Blood and/or mucus in stools
- Fatigue
- Weight loss and malnutrition
What signs do crohns patients present with?
Perianal lesions
Bowel obstruction i.e. abdominal bloating, distension, vomiting or constipation
What are the most common IBD symptoms?
abdominal pain or discomfort with diarrhoea or constipation.
What is calprotectin?
Calprotectin is 60% of cytosolic protein content in neutrophils
What is the role of neutrophils in the GI tract?
Neutrophils involved in inflammatory response in intestines
Why is calprotectin used as a marker for IBD?
Any disturbance in mucosal structure due to inflammatory response causes leakage of neutrophils and calprotectin
Calprotectin excreted in stools - measure levels in faces to assess inflammatory damage in bowels
How common us colorectal cancer?
Colorectal cancer is the third most common malignancy in the Western world.
It arises predominantly from adenomatous polyps
What are the signs of colorectal cancer?
Colorectal cancer is often asymptomatic until late-stage disease (poor prognosis).
Early detection greatly improves prognosis, and the condition is now routinely screened for in individuals > 60y
How do we test colorectal cancer?
Tests must detect blood in faeces - may be present in asymptomatic individuals with bowel lesions
Guaiac faecal occult blood (FOB) method widely used in screening.
How is blood in stools measured?
Dipstick test for blood in stool
Higher sensitivity than guaiac FOB method
