D-Xylose Excretion Test in Small Intestine
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Questions and Answers

What is the primary purpose of the D-xylose excretion test?

  • To assess vitamin B12 malabsorption
  • To evaluate small intestinal integrity (correct)
  • To diagnose protein-losing enteropathy
  • To assess pancreatic function

    • What is the normal faecal output of fat per day on a normal diet?

  • Up to 6 gram/day (correct)
  • Up to 12 gram/day
  • Up to 2 gram/day
  • Up to 10 gram/day

    • What is the mechanism of the 14C-triolein breath test?

  • 14C-labelled triglyceride is stored in the liver
  • 14C-labelled triglyceride is excreted in the stool
  • 14C-labelled triglyceride is degraded, releasing 14C-labelled CO2
  • 14C-labelled triglyceride is absorbed and metabolised, releasing 14C-labelled CO2 (correct)

    • What is the purpose of the Schilling test?

    <p>To diagnose vitamin B12 deficiency</p> Signup and view all the answers

    Which of the following is a characteristic of protein-losing enteropathy?

    <p>Increased faecal alpha-1-antitrypsin levels</p> Signup and view all the answers

    What is the normal range for faecal radioactivity in a normal individual?

    <p>+1%/day</p> Signup and view all the answers

    Which vitamin deficiency can be assessed by measuring the vitamin K-dependent prothrombin index?

    <p>Vitamin K</p> Signup and view all the answers

    What is the consequence of fat malabsorption on vitamin levels?

    <p>Decreased serum vitamin A and E levels</p> Signup and view all the answers

    What Liberates Vitamin B12 from Dietary R-Proteins?

    <p>Pancreatic Proteases</p> Signup and view all the answers

    What is the Primary Site of Vitamin B12 Absorption?

    <p>Terminal Ileum</p> Signup and view all the answers

    Which of the Following Enzymes is Not Involved in Protein Digestion?

    <p>Lipase</p> Signup and view all the answers

    What is the Result of Malabsorption of a Single Nutrient?

    <p>Deficiency of Only That Nutrient</p> Signup and view all the answers

    What is the Primary Cause of Malabsorption?

    <p>Defects in Both the Digestion and Absorption Phases</p> Signup and view all the answers

    What is the Consequence of Fat Malabsorption?

    <p>Fatty Stool</p> Signup and view all the answers

    What is the primary mechanism of malabsorption in Coeliac disease?

    <p>Mucosal dysfunction and uptake</p> Signup and view all the answers

    Which of the following is NOT a clinical feature of severe generalized malabsorption?

    <p>Hypertension</p> Signup and view all the answers

    What is the primary site of fat malabsorption in Crohn's disease?

    <p>Terminal ileum</p> Signup and view all the answers

    Which of the following vitamin deficiencies is commonly associated with malabsorption?

    <p>Vitamin B12</p> Signup and view all the answers

    What is the primary mechanism of malabsorption in Whipple's disease?

    <p>Abnormal lymphatics</p> Signup and view all the answers

    Which of the following is a non-GIT cause of malabsorption?

    <p>Hyperthyroidism</p> Signup and view all the answers

    What is the primary site of malabsorption in Cystic fibrosis?

    <p>Pancreas</p> Signup and view all the answers

    Which of the following is a clinical feature of malabsorption due to vitamin B12 deficiency?

    <p>Peripheral neuropathy</p> Signup and view all the answers

    Study Notes

    Small Intestine: CHO

    • D-xylose excretion test: ideal for small intestinal integrity
    • D-xylose is not normally present in the diet and is actively absorbed by the small bowel
    • >25% of the 5g oral dose is excreted in the urine within 5 hours
    • This test is unaffected by biliary or pancreatic disease

    Small Intestine: Proteins

    • Detect leakage of serum proteins into the bowel due to mucosal inflammation or lymphatic obstruction (protein-losing enteropathy)
    • Methods:
      • IV administration of 51Cr labelled albumin: faecal radioactivity >30%/day indicates protein-losing enteropathy
      • Measure faecal alpha-1-antitrypsin: directly proportional to plasma loss in the gut

    Fat/Lipids

    • Faecal fat excretion: normal output is up to 6g/day on a normal diet of 100g fat/day
    • Increased excretion is seen in:
      • Generalized small bowel disease
      • Pancreatic insufficiency
      • Biliary obstruction
      • Terminal ileal disease/resection
    • 14C-triolein breath test: decreased excretion of 14CO2 indicates fat malabsorption

    Assessment for Vitamins

    • Serum Vitamin A and E levels are decreased in fat malabsorption
    • Vitamin A, E, and D levels can be requested
    • Vitamin K deficiency is assessed by measuring the Vitamin K-dependent prothrombin index

    Vitamin B12 Malabsorption

    • Suspicion of Vitamin B12 malabsorption: clinical features (fatigue/weakness, peripheral neuropathy), megaloblastic anaemia, low Vit B12
    • Schilling test: 1ug 58Co labelled vitamin B12 is given orally with a large 1mg intramuscular dose of unlabelled B12

    Digestion and Absorption

    • Monosaccharides (glucose, fructose, galactose) are absorbed into enterocytes
    • Digestion and absorption of proteins:
      • Mouth: pepsin cleaves internal bonds of proteins
      • Stomach: digestion proceeds further through pancreatic proteases
      • Small intestine: mixtures of amino acids, dipeptide, and tripeptides are absorbed into the blood
    • Digestion and absorption of fats:
      • Binds to salivary and dietary R-proteins
      • R-proteins are digested by pancreatic proteases, liberating B12
      • Binds to IF and is absorbed in the terminal ileum

    Malabsorption

    • May occur due to defects in digestion or absorption phase
    • Single nutrient or multiple nutrients may be affected
    • 3 phases of digestion/absorption:
      • Luminal
      • Mucosal
      • Post-absorptive

    Defects in Digestion and Absorption

    • Luminal: decreased lipase/protease secretion (e.g., chronic pancreatitis, intestinal resection, bile duct obstruction, cystic fibrosis)
    • Mucosal: mucosal dysfunction (e.g., coeliac disease, disaccharides deficiency)
    • Post-absorptive: abnormal lymphatics (e.g., intestinal lymphangiectasia, Whipple's disease)

    Clinical Features

    • Severe generalised malabsorption:
      • Diarrhoea
      • Steatorrhoea
      • Weight loss
      • Flatulence and abdominal distension
      • Anaemia (iron deficiency/megaloblastic)
      • Oedema
      • Metabolic bone disease
      • Features of vitamin deficiencies (e.g., skin lesions, peripheral neuropathies, petechial haemorrhages)
      • Neurological manifestations

    Malabsorption Syndromes

    • Coeliac disease (small intestine)
    • Cystic fibrosis (pancreas)
    • Crohn's disease (small intestine, including terminal ileum)
    • Whipple's disease (small intestine + lymphatics)
    • Intestinal parasites
    • Short bowel syndrome

    Non-GIT Causes of Malabsorption

    • Hyperthyroidism
    • Hypothyroidism
    • Addison's disease
    • Carcinoid syndrome

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    Description

    This quiz is about the D-xylose excretion test, a method to evaluate small intestinal integrity. It assesses intestinal malabsorption by measuring the urinary excretion of D-xylose after an oral dose.

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