Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (139 page)

   
Hormonal studies
: TSH, fasting serum gastrin level, calcitonin level, and 24-hour urine collection for 5-hydroxy indole acetic acid (5-HIAA) are recommended.

   
D
-xylose testing
: This tests for small bowel malabsorption syndromes (e.g., sprue, Crohn disease, amyloidosis). Twenty-five grams of
D
-xylose
are administered. A 5-hour urine collection and a 1-hour serum sample are obtained. A decreased amount of
D
-xylose
in the urine and serum indicates small bowel malabsorption. The sensitivity of the test is decreased in the following situations: creatinine clearance of <30 mg/dL, portal hypertension, ascites, delayed gastric emptying, fiber supplements, glucose load, aspirin, and glipizide.

   
Bentiromide test
(to test for pancreatic exocrine insufficiency):
N
-benzoyll-tyrosyl para-aminobenzoic acid (NBT PABA) is administered orally. The molecule is cleaved by chymotrypsin; PABA is absorbed and then measured in a 6-hour urine collection. PABA alone is a somewhat inaccurate measure, so additional markers have been used to increase the accuracy.

   
Serum immune markers
: Several serum immune markers performed by ELISA have been found to be valuable for the diagnosis, stratification, and management of IBD (see Celiac Disease):

   Deoxyribonuclease (DNAse)-sensitive perinuclear antineutrophil cytoplasmic antibody (P-ANCA) is positive in 60–80% of adults with ulcerative colitis (UC) and in 83% of children with UC. P-ANCA is positive in 10% of patients with Crohn disease.

   Anti-
Saccharomyces cerevisiae
antibody (ASCA) is present in 70% of patients with Crohn disease.

   Pancreatic antibody may be positive in 30–40% of patients with Crohn disease.

   Outer membrane porin from
E. coli
(OmpC) antibody: An immunoglobulin A (IgA) response to OmpC is seen in 55% of patients with Crohn disease.

   Lactoferrin, stool: A sensitive and specific marker for detecting inflammation or from irritable bowel syndrome (IBS) once infectious causes of inflammation and colorectal cancer are ruled out.

   Calprotectin for screening of patients with diarrhea to help distinguish between active IBD and IBS.

DIARRHEA, ACUTE

OSMOTIC DIARRHEA

   Definition

Defined as diarrhea with a <3-week (upper limit 6–8 weeks) duration. Increased osmotically active solutes in the bowel; diarrhea usually stops during fasting.

Causes

   Exogenous