day 4 - Gut malabsorption Flashcards
The causes of malabsorption can be grouped as follows:
The causes of malabsorption can be grouped as follows:
• Impaired Digestion - pancreatic disease; biliary obstruction; gastrectomy; enzyme
defects.
- Impaired Absorption - coeliac disease; intestinal resection; malignant infiltration.
- Bacterial Overgrowth - blind loops; stasis.
- Abnormal Transit Times - post gastrectomy; endocrine tumours.
Malabsorption states can also be classified into generalised, where all major nutrient classes are involved (common!), or specific, when only a single nutrient or nutrient group is affected. The latter type is less common but includes problems arising from:
- Lack of cofactor eg intrinsic factor (B12).
- Lack of transport system eg Hartnup disease (certain amino acids).
- Lack of enzyme eg lactase (lactose).
- Site specific disease eg terminal ileum (B12).
Is There Malabsorption?
• History: age, weight loss, duration of symptoms, previous travel, antibiotic therapy,
alcohol intake etc.
• Stool Appearance: volume, consistency, colour.
• Basic Blood Tests: bone profile, albumin, haemoglobin (B12; folate; Fe), prothrombin
time.
- Special Tests (Non specific): usually assess fat absorption. Include:
- Faecal Fat
- > 18 mmol/24h = ? malabsorption
- Variable transit times/rectal emptying are major sources of error (use of markers?) - Minimum collection period is 3 days
- Unnecessary if obvious steatorrhoea
- Unpleasant for all!
- NO INDICATION OF CAUSE
• 14C Triolein Breath Test - Rapid (2-8h)
- Assumes constant CO2 production (? endocrine disease) - Not suitable in children, pregnancy, COAD
- Limited availability (beta emitting isotope)
- NO INDICATION OF CAUSE
specific tests exist for specific defects and must be employed as necessary eg
cystic fibrosis (sweat electrolytes); enzyme deficiencies (loading tests, brush border biopsy and enzyme assay).
Pancreatic Function tests
• Tube Tests:
- Assay of enzymes/HCO3/volume in duodenal juice following pancreatic stimulation
via test meal (Lundh Test) or combined secretin/cholecystokinin injection. - Invasive and little used today!
• Tubeless Tests:
- Feed synthetic substrate needing hydrolysis by pancreatic enzymes.
- Products of digestion are measured in urine.
- Need to correct for variations in renal and absorptive function.
- Non invasive
- ‘PABA’ and ‘Pancreolauryl’ tests are common examples, the latter being technically simpler
test of Small Intestinal Function
• Xylose Absorption Test
- Tests jejunal absorptive capacity
- Oral xylose absorbed and excreted unchanged in the urine
- Interpretive problems in presence of low GFR, delayed gastric emptying, oedema
and inaccurate urine collections
- Blood levels can aid interpretation and are essential in young children
Detection of Bacterial Overgrowth
• 14C Glycocholate Breath Test
- Labelled glycocholate (a bile salt) given orally
- Excessive bacterial deconjugation yields 14C glycine which is metabolised to 14C
CO2
- Problems as for 14C triolein test
- 14C-glycocholate breath test Bacterial deconjugation of bile salts causes fat malabsorption via impaired micelle formation
- Measure 14CO2 in breath
Diagnosis of Acute Pancreatitis
- Common causative factors include gall stones and alcohol abuse. More rarely chronic hypercalcaemia or hypertriglyceridaemia may be implicated.
- Biochemical diagnosis based on demonstration of elevated plasma amylase, usually to >10x upper limit of normal. Once the diagnosis is made, further plasma amylase measurements are rarely necessary!
• BEWARE other causes of hyperamylasaemia (although usually of lesser magnitude) which include:
- Other acute abdominal emergencies (perforated ulcer; ruptured ectopic)
- Diabetic ketoacidosis
- Renal failure (reduced amylase clearance)
- Mumps (salivary amylase)
- Macroamylaseaemia (permanently raised levels due to circulating amylase/IgG complex). A harmless condition.
Neuroendocrine Tumours of the Gut
Two examples are outlined.
Carcinoid Syndrome
• Most carcinoid tumours occur in the gut
• Symptoms (flushing, diarrhoea, borborygmi, wheezing) usually associated with presence of liver metastases or foregut tumours (eg lung), when tumour products are secreted directly into systemic circulation. These include tryptophan metabolites (serotonin etc.) and various peptides.
• Diversion of tryptophan to serotonin synthesis can cause pellagra like syndrome.
• Diagnose and monitor via urine 5-hydroxyindoleacetic acid (5HIAA) excretion.
Gastrinoma (Zollinger-Ellison Syndrome)
• Usual sites are pancreas and duodenum - 60 % are malignant
• May be part of multiple endocrine neoplasia (MEN) syndrome
• Hypersecretion of gastric acid causes severe ulceration and malabsorption
• Plasma gastrin levels aid diagnosis but note other causes of hypergastrinaeamia
including H2 blocker therapy.
• PTH is released from parathyroid glands in response to:
- A fall in plasma ionised Ca (most important)
- A rise in plasma phosphate (chronic effect only)
• Target organs of PTH are:
Kidney: Increases Ca reabsorption Decreases PO4 reabsorption
Decreases HCO3 reabsorption
Increased Vit D activation (1 hydroxylation)
Bone: Increases osteoclastic resorption
causes of hypercalcaemia
Causes
• Common
• Others
Simple Guide
- Primary hyperparathyroidism (prevalence 1/1000) - Malignant disease (including myeloma)
- Bony metastases
- Tumour synthesis of PTH related peptide
- Tumour synthesis of other hypercalcaemic agents
- Sarcoidosis (increased calcitriol synthesis)
- Vitamin D intoxication
- Tertiary hyperparathyroidism (eg chronic renal failure → post
Tx)
- Immobilisation (Pagets, adolescents)
- Thyrotoxicosis, if severe
- Thiazide diuretics
- Familial hypocalciuric hypercalcaemia (very rare)
• Hypercalcaemia + suppressed PTH = non-parathyroid cause
• Hypercalcaemia + raised (or detectable) PTH = PTH mediated cause
causes of hypocalcaemia
Causes (but beware hypoalbuminaemia)
• Vitamin D deficiency.
• Disordered vitamin D metabolism (eg renal failure).
• Hypoparathyroidism (congenital; autoimmune; post thyroid surgery; infiltrations).
• Pseudohypoparathyroidism (PTH resistance).
• Magnesium depletion (impaired PTH synthesis/release).
• Acute pancreatitis.
• Neonatal.
• Massive blood transfusion (citrated blood).
Gut malabsorption Page 6

Simple Guide
• Hypocalcaemia + low/undetectable PTH = hypoparathyroidism.
• Hypocalcaemia + elevated PTH = non-parathyroid cause (except pseudo hypo-
parathyroid).
what is PARENTERAL NUTRITION
Parenteral nutrition (PN) is feeding a person intravenously, bypassing the usual process of eating and digestion. The person receives nutritional formulae that contain nutrients such as glucose, amino acids, lipids and added vitamins and dietary minerals.
