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CP > Lab Investigation of Diarrhoea and Malabsorption > Flashcards

Lab Investigation of Diarrhoea and Malabsorption Flashcards

1
Q

Diarrhoea

A

> 200g/day

Acute = <2 weeks
Persistent = 2-4 weeks
Chronic = >4 weeks
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2
Q

Acute diarrhoea classification

A

Sudden alteration in frequency or liquidity of stool
90% infectious

Inflammatory

  • damage to intestinal mucosal barrier by direct invasion or cytotoxins e.g. CHESS organisms, entamoeba, IBD
  • cramps, urgency, +/- fever
  • stool: bloody, small volume
  • stool exam: leukocytes and RBC +++

Non-Inflammatory

  • no disruption or damage to intestinal epithelium e.g. virus, enterotoxic bacteria, IBS, food intolerance
  • no pain or fever
  • stool: watery with no blood
  • stool exam: leukocytes absent
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3
Q

Investigation of acute diarrhoea

A

Not routinely done due to self limiting nature of disease

Only indicated if:

  • severe dehydration, recent antibiotic use, bloody stools, fever, severe pain etc.
  • detect complications

Ix:

  • stool: culture, microscopy for parasites, viral studies, C. difficile toxin
  • colonoscopy with biopsy
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4
Q

Chronic diarrhoea classifications

A

Mostly non-infectious

Secretory, Osmotic, Steatorrhea, Dymotility, Inflammatory

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5
Q

Secretory: manifestation, cause, lab results

A

Derangement in fluid and electrolyte transport across mucosa

Painless watery large volume outputs
Persists with fasting

Causes
- stimulant laxative, cholera, bowel resection, VIPoma, carcinoid

Lab
- suppressed stool osmolal gap (290-2x{Na + K} <50 mOsm/kg)

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6
Q

Osmotic: manifestation, cause, lab results

A

Poorly absorbable, osmotically active solutes draw fluid into lumen exceeding reabsorptive capacity of colon

Ceases with fasting

Causes
- osmotic laxative, lactase/ disaccharidase deficiencies, non-absorbable carbohydrates e.g. sorbitol, lactulose, PEG

Lab
- elevated stool osmolal gap >100 mOsm/kg

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7
Q

Steatorrhea: manifestation, cause

A

Fat malabsorption

Greasy, foul-smelling, difficult to flush diarrhoea
a/w weight loss and nutritional deficiencies

(osmotic effects of fatty acids)

Causes

  • intraluminal maldigestion e.g. exocrine pancreatic insufficiency, bacterial overgrowth
  • mucosal malabsorption e.g. celiac disease, Whipple’s disease
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8
Q

Dysmotility: cause

A

Rapid transit of GI contents

Causes
- hyperthyroidism, IBS

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9
Q

Inflammatory: manifestation, cause, lab results

A

Exudation, disrupted fluid/electrolyte absorption, inflammatory mediators

Pain, fever, bleeding, other manifestations of inflammation

Causes
- IBD, GI malignancies

Lab
- fecal calprotectin increased (distinguish inflammatory and non-inflammatory causes)

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10
Q

Diagnostic approach for chronic diarrhoea

A
  1. Hx, P/E, basic tests (CBC, RLFT, thyroid function etc.)
  2. Studies for acute diarrhoea (microbiology)
  3. Specific tests
    - endocrine e.g. hormone secreting tumours (urine 5-HIAA, fasting serum VIP/ gastrin)
    - faecal occult blood
    - faecal calprotectin
    - urine laxative screen
    - specific tests for malabsorption or steatorrhea e.g. faecal elastase, CT pancreas, small bowel biopsy
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11
Q

Normal physiology of absorption and specific requirements for absorption of certain substances

A

Normal digestion/absorption:

  • speed of passage
  • absorbable forms of nutrients
  • intestinal mucosa

Specific requirements:

  • lipid – bile, lipase
  • carbohydrate – amylase, disaccharidase
  • protein – pepsin, trypsin, chymotrypsin
  • B12 - IF, intestinal flora (consume B12), lower ileum
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12
Q

Generalised malabsorption

A 
Pancreatic dysfunction (digestion)
- chronic pancreatitis, fibrocystic disease of pancreas, inactivation of lipase by Zollinger-Ellison syndrome

Intestinal disease (absorption)

  • reduced absorptive surface/ impaired transport e.g. celiac disease, tropical sprue
  • extensive infiltration or inflammation e.g. Crohn’s, amyloidosis
  • increased rate of passage e.g. carcinoid syndrome, post-gastrectomy
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13
Q

Malabsorption of specific substances

A

Altered bacterial flora e.g. blind-loop syndrome (stasis causing overgrowth), diverticula, surgery
–> fat (bile salts deconjugated), B12

Biliary obstruction
–> fat and substances dependent on fat absorption e.g. fat-soluble vitamins

Local disease or surgery
–> B12 in terminal ileum resection/ Crohn’s

Gastric atrophy e.g. pernicious anaemia
–> B12

Disaccharidase deficiency e.g. congenital or acquired
–> carbohydrates

Protein-losing enteropathy

Isolated transport defects from IEM

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14
Q

Manifestations of generalised malabsorption: fat, vitamins, protein, carbohydrates

A

Fat

  • steatorrhea, bulky/gray/soft/sticky/foul-smelling stools
  • fat-soluble vitamin malabsorption
  • lab: fractional fat excretion >6%

Fat-soluble vitamins and Ca

  • hypovitaminosis D impairs Ca absorption –> hypoCa, secondary hyperPTH, high ALP
  • hypovitaminosis K –> bleeding with prolonged PT
  • hypovitaminosis A –> night blindness, dermatitis (rarely clinically evident)

Protein

  • muscle atrophy
  • oedema (less albumin)
  • recurrent infection (less Ab)

Carbohydrate

  • flat OGTT or imparted polysaccharide absorption (intestinal and pancreatic)
  • osmotic diarrhoea, flatulence, high stool osmolar gap
  • lab: increased H2 breath test
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15
Q

Manifestations of specific malabsorption: B12 and lactase deficiency

A

B12

  • megaloblastic anaemia, peripheral neuropathy, glossitis
  • lab: increased MCV, serum homocysteine and MMA increased, decreased B12

Lactase deficiency
- severe diarrhoea with typically acid stools

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16
Q

Biochemical tests

A

(in addition to stool culture/ microscopy to rule out infective causes)

Possible findings (not always present in mild cases):

  • CBC – anaemia
  • LFT - biliary cholestasis
  • low vitamin B12/ folate/ iron
  • low Ca/ PO4
  • high ALP
  • low total proteins/ albumin
  • prolonged PT
  • abnormal thyroid function
17
Q

Specific biochemical tests for fat absorption

A
  1. Qualitative stool exam
    - fat-soluble stain e.g. Sudan III
    - false positives e.g. orlistat, mineral oils
  2. Faecal fat quantitation
    - 3-5 days collection required for reliable results
    - compliance, collection and storage issues

==> steatorrhea generally a circumstantial Dx (most labs no longer do testing)

18
Q

Specific biochemical tests for carbohydrate absorption

A
  1. Oral sugar tolerance test
    - administer test sugar and measure blood glucose concentrations over time
    - no rise = malabsorption
    - MUCOSAL dysfunction because none of the sugars depend on pancreatic enzymes or bile for absorption
  2. Hydrogen breath test
    - fasting patients given sugar solution –> not absorbed in small intestine –> fermented by colonic bacteria which produces hydrogen –> absorbed in bloodstream and exhaled in breath
    - take breath samples Q30min for 2.5 hrs
    - diagnostic if positive; POCT/ lab
19
Q

Disaccharidase deficiency: Sx, Dx and Tx

A

Symptoms
- diarrhoea (osmotic), failure to thrive, abdominal distension and pain (flatulence due to bacteria fermentation)

Diagnosis

  • dietary exclusion
  • endoscopy with biopsy and measurement of enzymes
  • hydrogen breath test

Treatment
- avoid foods containing specific disaccharide

20
Q

Specific biochemical tests for small intestine bacterial overgrowth

A
  1. Hydrogen breath test
    - bolus of glucose ingested and measure breath hydrogen concentrations sequentially
    - presence of bacteria in the small intestine = glucose fermented before it is absorbed and hydrogen produced
    - non-specific (can only confirm SIBO if symptoms disappear after treating and eradicating bacteria)
  2. Quantitative culture of jejunal aspirate
    - gold standard but more dangerous and complex
21
Q

Disorders a/w bacterial overgrowth

A

Small intestinal stasis

  • anatomic abnormalities e.g. diverticulosis, surgically created blind-loops, strictures
  • abnormal motility e.g. DM, scleroderma

Abnormal communication between proximal and distal GI tract
- gastrocolic and jejunocolic fistula

A/w multifactorial causes
- immunodeficiency, chronic pancreatitis, cirrhosis, ESRD

22
Q

Specific biochemical tests for B12 absorption

A
  1. Serum B12 & folate; plasma homocysteine and methymalonic acid as second line Ix
  2. Anti-parietal cell and anti-IF Ab; high serum gastrin levels; Schilling test
    - Dx of pernicious anaemia (need parenteral or IM B12 to treat!)
23
Q

Vitamin B12 deficiency causes and symptoms/signs

A

Possible causes:

  • lack of IF (pernicious anaemia)
  • gastrectomy
  • chronic pancreatitis
  • bacterial overgrowth in jejunum
  • ileum resection/ Crohn’s disease

Suspect if:

  • macrocytic anaemia, hypersegmented neutrophils, pancytopenia
  • peripheral neuropathy/ unexplained neurological signs
  • elderly/ alcoholic/ strict vegan/ malnutrition
  • previous bariatric surgery
24
Q

Schilling test (no longer used now)

A

Part I: radioactive B12 PO and IM flushing dose of non-radioactive B12 within 2 hrs (saturate body stores)
–> 24 hr urine collection and radioactivity measured (normal body should absorb radioactive B12 and excrete it)

Part II: radioactive B12 + IF PO, flushing dose of non-radioactive B12
–> measure urine radioactivity

Results:

  • Part I and II low = intestinal malabsorption at terminal ileum
  • Part I low and II normal = pernicious anaemia

(modified schilling - part III repeat after antibiotics to Dx SIBO)
- assume adequate renal function, pancreatic exocrine function and no bacterial overgrowth of gut

25
Q

Other tests

A

Radiological studies to aid diagnosis e.g. pancreas

Endoscopy with biopsy

  • mucosal biopsy for panmalabsorption to identify or exclude diffuse mucosal disease
  • aspirate jejunal contents
26
Q

Celiac disease: cause, Sx, Dx, Tx

A

Rare in Chinese
Gluten sensitive enteropathy

  • autoimmune, inflammatory disorder triggered by ingestion of gluten
  • diarrhoea, steatorrhea, weight loss, abdominal pain, flatulence, fatigue, failure to thrive

Ix:

  • anti-tissue transglutaminase Ab
  • HLA-DQ2 or DQ8
  • small bowel biopsy is gold standard

Dx confirmed if Sx relieved after gluten free diet

Tx: gluten free diet

27
Q

Cystic fibrosis: cause, Sx, Dx, Tx

A

Congenital metabolic disorder with abnormal exocrine gland secretions

Sx
- failure to thrive, chronic respiratory infections, malabsorption

Dx

  • newborn screening: immunoreactive trypsinogen
  • CFTR gene test
  • sweat test
  • faecal trypsin, chymotrypsin or elastase (assess pancreatic exocrine insufficiency)

Tx
- antibiotics, enzyme replacement, physiotherapy

CP (37 decks)

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