Malabsorption Flashcards
What is assimilation vs maldigestion?
Maldigestion - defects in digestion (actual breaking down of food)
Assimilation - another name for absorption, process by which food is taken up after digestion
What role does the pancreas play in absorption of B12?
Proteases are required to remove R-binder from B12
How can fat malabsorption cause kidney stones?
Calcium normally binds oxalate in small intestine so it precipitates out and cannot be absorbed
If there are too many free fatty acids, they bind calcium as soaps, making oxalate available for for colonic absorption
Hyperoxaluria leads to stones
How does bile salt malabsorption cause gallstones?
If not absorbed in the distal ileum, lack of bile salts will allow cholesterol to precipitate out in the bile and form stones
What are the premucosal / luminal causes of malabsorption?
Pancreatic insufficiency Hepatobiliary disease Bacterial overgrowth Rapid intestinal transit Gastrectomy
What are a couple post-mucosal causes of malabsorption? What will biopsy show?
Congenital lymphangiectasia, secondary lymphangiectasia
Biopsy shows clear dilated lacteals in intestinal villi
What is a specific test of malabsorption given a patient is eating normal amounts of fruits and vegetables?
Serum carotene
How are fats normally absorbed in the GI tract?
Lipolysis occurs via pancreatic lipases, cleaving triglycerides to beta-monoacylglycerides + fatty acids
Fatty acids / MAGs are solubilized by bile salts into micelles, diffuse across cell membrane
Fatty acids / MAGs are remade into triglycerides, packed into chylomicrons and then shipped through the lacteals into the venous system
What is given patients if they have fat malabsorption and why?
Medium chain triglycerides
- > no lipolysis needed
- > no micelle formation needed (freely diffuse)
- > high rate of absorption, with no need to form chylomicrons
- > uptaken into bloodstream, not lymphatics (good if lymphatic failure)
Give two tests for assessing fat malabsorption (one rapid, one more extensive)
Rapid - Sudan stain to see qualitative amount of fat in stool
72-hour fecal fat collection - monitor fat intake for 72 hours and measure fat concentration in stool (collect in a coffee jar). if <94% of fat has been absorbed, that’s abnormal
Give three causes of exocrine pancreas insufficiency?
- Chronic pancreatitis
- Cystic fibrosis
- Pancreatic tumors obstructing release
What is the bentiromide test for pancreatic insufficiency? Problem?
Give patient PABA linked to bentiramide -> if chymotrypsin is present, PABA will be reabsorbed. PABA will show up in urine if pancreas is functioning properly.
Problem - test can also be positive if small bowel absorption is diminished (no PABA reabsorbed)
What is the secretin stimulation test for pancreatic insufficiency?
Collected intestinal juices after giving IV secretin
If bicaronate response is low, this suggests pancreatic insufficiency
What is the primary modality used to diagnose pancreatic insufficiency?
Imaging - i.e. ERCP, MRCP, ultrasound, EUS, and CT
-> look for obstruction of pancreatic duct causing the issue
How is pancreatic insufficiency empirically determined?
Trial of pancreatic enzyme replacement -> if this helps, insufficiency is likely
What is the D-xylose test and what is it checking for? Is it affected by pancreatic insufficiency?
Give patient D-xylose, which is passively absorbed in small intestine. Normal test is about 25% of given xylose showing up in the urine.
Causes for decreased blood or urine levels of xylose include:
- Decreased small bowel absorptive capacity (i.e. Celiac’s)
- Bacterial overgrowth -> before it reaches the small bowel
Passively reabsorbed so not affected by pancreatic insufficiency
Give a cause of B12 deficiency that isn’t pernicious anemia, gastrectomy, ileal disease, or pancreatic insufficiency.
Bacterial overgrowth - bacteria can eat up all the B12
How do you test for lactose deficiency via breath test? How do you get a baseline?
Hydrogen breath test
-Give lactose. A greater than 20 PPM rise over several hours in breath hydrogen is noted if you have lactose deficiency. This is because lactose hits your colonic bacteria who ferment it.
baseline is given via lactulose which is always fermented if there is some question of the result
Other than B12, what other deficiencies can bacterial overgrowth cause? What are the symptoms?
Fat malabsorption - due to deconjugation of bile salts
Direct damage to mucosal epithelium
Iron deficiency
SCFA production and carbohydrate fermation in colon -> diarrhea, gas, cramping
Give three ways to diagnose bacterial overgrowth.
- Hydrogen breath test with any sugar leads to a peak within 30-60 min
- Quantitative and qualitative colony counts via aspirated jejunal fluid
- Trial of antibiotics improving symptoms
What are the causes of bacterial overgrowth?
Achlorhydria, and things which alter GI system structure or motility
Structure - i.e. gastric surgery with blind loops, fistulas, strictures, diverticulosis, ileocecal valve loss
Motility - i.e. scleroderma, diabetes
What are the imaging and biopsy techniques to test for malabsorption in generaly?
Small bowel CT enterography or X-ray
Small bowel enteroscopy and biopsy
Wireless capsule endoscopy (swallow a camera pill)
What is a celiac serology?
IgA and IgG titers for anti-Tissue Transglutaminase antibodies (highly sensitive)
Anti-endomysial antibodies
Anti-gliadin antibodies
How does HIV predispose to malabsorption?
Predisposes to many parasitic infections which can cause malabsorption
-> HIV testing may be part of a standard workup
What must you give with pancreatic enzyme replacement therapy?
PPIs -> enzymes will be inactivated with acidic pH
What diet can be given to treat someone with a brush border enzyme defect?
Elemental diets -> things which are easily absorbed (i.e. no complex sugars or proteins)
