Malabsorption

Question 1

What is assimilation vs maldigestion?

Answer 1

Maldigestion - defects in digestion (actual breaking down of food)

Assimilation - another name for absorption, process by which food is taken up after digestion

Question 2

What role does the pancreas play in absorption of B12?

Answer 2

Proteases are required to remove R-binder from B12

Question 3

How can fat malabsorption cause kidney stones?

Answer 3

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

Question 4

How does bile salt malabsorption cause gallstones?

Answer 4

If not absorbed in the distal ileum, lack of bile salts will allow cholesterol to precipitate out in the bile and form stones

Question 5

What are the premucosal / luminal causes of malabsorption?

Answer 5

Pancreatic insufficiency
Hepatobiliary disease
Bacterial overgrowth
Rapid intestinal transit
Gastrectomy

Question 6

What are a couple post-mucosal causes of malabsorption? What will biopsy show?

Answer 6

Congenital lymphangiectasia, secondary lymphangiectasia

Biopsy shows clear dilated lacteals in intestinal villi

Question 7

What is a specific test of malabsorption given a patient is eating normal amounts of fruits and vegetables?

Answer 7

Serum carotene

Question 8

How are fats normally absorbed in the GI tract?

Answer 8

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

Question 9

What is given patients if they have fat malabsorption and why?

Answer 9

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)

Question 10

Give two tests for assessing fat malabsorption (one rapid, one more extensive)

Answer 10

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

Question 11

Give three causes of exocrine pancreas insufficiency?

Answer 11

1. Chronic pancreatitis
2. Cystic fibrosis
3. Pancreatic tumors obstructing release

Question 12

What is the bentiromide test for pancreatic insufficiency? Problem?

Answer 12

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)

Question 13

What is the secretin stimulation test for pancreatic insufficiency?

Answer 13

Collected intestinal juices after giving IV secretin

If bicaronate response is low, this suggests pancreatic insufficiency

Question 14

What is the primary modality used to diagnose pancreatic insufficiency?

Answer 14

Imaging - i.e. ERCP, MRCP, ultrasound, EUS, and CT

-> look for obstruction of pancreatic duct causing the issue

Question 15

How is pancreatic insufficiency empirically determined?

Answer 15

Trial of pancreatic enzyme replacement -> if this helps, insufficiency is likely

Question 16

What is the D-xylose test and what is it checking for? Is it affected by pancreatic insufficiency?

Answer 16

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:

1. Decreased small bowel absorptive capacity (i.e. Celiac’s)
2. Bacterial overgrowth -> before it reaches the small bowel

Passively reabsorbed so not affected by pancreatic insufficiency

Question 17

Give a cause of B12 deficiency that isn’t pernicious anemia, gastrectomy, ileal disease, or pancreatic insufficiency.

Answer 17

Bacterial overgrowth - bacteria can eat up all the B12

Question 18

How do you test for lactose deficiency via breath test? How do you get a baseline?

Answer 18

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

Question 19

Other than B12, what other deficiencies can bacterial overgrowth cause? What are the symptoms?

Answer 19

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

Question 20

Give three ways to diagnose bacterial overgrowth.

Answer 20

1. Hydrogen breath test with any sugar leads to a peak within 30-60 min
2. Quantitative and qualitative colony counts via aspirated jejunal fluid
3. Trial of antibiotics improving symptoms

Question 21

What are the causes of bacterial overgrowth?

Answer 21

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

Question 22

What are the imaging and biopsy techniques to test for malabsorption in generaly?

Answer 22

Small bowel CT enterography or X-ray

Small bowel enteroscopy and biopsy

Wireless capsule endoscopy (swallow a camera pill)

Question 23

What is a celiac serology?

Answer 23

IgA and IgG titers for anti-Tissue Transglutaminase antibodies (highly sensitive)
Anti-endomysial antibodies
Anti-gliadin antibodies

Question 24

How does HIV predispose to malabsorption?

Answer 24

Predisposes to many parasitic infections which can cause malabsorption
-> HIV testing may be part of a standard workup

Question 25

What must you give with pancreatic enzyme replacement therapy?

Answer 25

PPIs -> enzymes will be inactivated with acidic pH

Question 26

What diet can be given to treat someone with a brush border enzyme defect?

Answer 26

Elemental diets -> things which are easily absorbed (i.e. no complex sugars or proteins)