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AD 11/02
Chronic Diarrhea
When and how to evaluate for chronic diarrhea?
! Patients with > 4 weeks of diarrhea should be evaluated for chronic diarrhea. After 4
weeks, most acute infectious enteritides will have resolved.
! Take a good history and physical. Ask about duration, frequency, blood, travel history,
relation of food to diarrhea, medications, other systemic symptoms.
! Consider these broad categories: malabsorptive, secretory, inflammatory, motility,
infectious.
! The proposed stepwise evaluation has two outpatient stages, followed by a third inpatient
stage if necessary (i.e. not necessary to send lots of elaborate tests right away). Authors
state that this approach leads to a diagnosis in 90% of cases.
Preliminary workup:
•Confirm that patient truly has diarrhea: more than 300 gm stool weight in 24 hours.
•Prescribe a lactose-free diet for several days to rule out secondary lactase deficiency, which is
common after an acute episode of diarrhea.
•Test for HIV in the appropriate clinical setting (this article applies to non-HIV infected cases).
•Correct dehydration while the workup is proceeding.
Stage one - outpatient evaluation
•History and limited labs to identify common causes of chronic diarrhea. The following work-up
should be tailored to the individual.
Lactose free diet supervised by nutritionist: to rule out lactase deficiency.
Fecal wbc (inflammatory), stool O&P, C. dif toxin.
Common infectious causes include:
giardia: upper abdominal cramps, “frothy” stool. Sensitivity of O&P x 3 is 60-85%.
amebiasis: watery or bloody stool, +/- fecal WBCs. Sensitivity of O&P x 3 is 60-90%.
Stool pH: carbohydrate intolerance (due to viral enteritis with small intestinal mucosal
damage, or due to antibiotics, which alter gut flora) causes bloating, flatus, cramping.
Stool pH <5.3 is diagnostic.
24 hr fecal fat: must be performed with patient on strict diet of 75-100 gm/24 hrs. Normal
excretion is <7 gm fat/24 hrs. Historical clues of steatorrhea: weight loss, greasy
malodorous stools that are difficult to flush.
LABS: CBC, lytes, TSH, albumin, coags, beta-carotene Consider VIP if diarrhea >1
liter/dy.
KUB: to rule out pancreatic calcification (chronic pancreatitis).
Flex sig: to rule out inflammatory bowel disease, lymphocytic colitis. Barium studies if neg.
Stage two - outpatient evaluation
•Most inflammatory and malabsorptive causes of diarrhea have been ruled out.
Laxative abuse moves up on the list of DDx - 4% of all GI referrals for chronic diarrhea, up
to 20% at tertiary centers. Many tests are available to rule out laxative abuse, but
physicians generally underscreen for this etiology of diarrhea.
EIA for giardia (remember, O&P sensitivity only 60-85%).
AD 11/02
Colonoscopy, small bowel biopsy: to rule out Crohn’s, other right-sided colitis,
amebiasis.
Stage three - inpatient evaluation
•Again, common disorders are at the top of the list: laxative abuse and inflammatory bowel
disease that were missed during the outpatient workup.
•Confirm again that diarrhea is present- stool weight >300 gm/24 hrs on regular diet.
•72 hour fast with IV hydration: to differentiate osmotic from secretory diarrhea
Osmotic: •Diarrhea stops during fasting
•Therefore something in the diet is causing the diarrhea
•Check stool osmolar gap (normally should be <50 mOsm/kg)
Stool osm gap = 2(stool Na + stool K) – 290
In osmotic diarrhea, osm gap will be >50 mOsm/kg.
•DDx: laxative abuse (non-absorbable anion such as sodium citrate, Mg)
malabsorption of carbohydrates, bile acids, or fatty acids
Secretory: •No/minimal response to fasting after 48 hrs
•Stool osm gap normal at <50 mOsm/kg
•DDx: laxative abuse, inflammatory bowel disease, giardia, amebiasis,
bacterial overgrowth
rare disorders: sprue, neuroendocrine tumors, intestinal lymphoma
Summary
In a patient with chronic diarrhea,
(1) Confirm that stool weight is in fact >300 gm/24 hrs
(2) Lactose free diet to rule out lactase deficiency from recent acute diarrhea
(3) Rule out common disorders:
chronic infection (giardia, amebiasis, C.Dif)
inflammatory bowel disease
fat/carbohydrate malabsorption
laxative abuse
References:
Donowitz M. Evaluation of patients with chronic diarrhea. New England Journal of Medicine. 1995;332;725-9.
AGA guidelines on chronic diarrhea.
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