Laboratory Evaluation for Chronic Diarrhea

Initial Laboratory Workup

The American Gastroenterological Association recommends comprehensive laboratory testing, including stool studies for Giardia, fecal calprotectin or lactoferrin, and serological testing for celiac disease, along with basic blood work to evaluate for inflammatory, metabolic, and nutritional abnormalities in patients with chronic diarrhea 1, 2
Complete blood count (CBC), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), basic metabolic panel, liver function tests, calcium, vitamin B12, folate, iron studies, and thyroid function tests should be included in the initial laboratory workup for patients with chronic diarrhea 3, 4
The European Society for Pediatric Gastroenterology, Hepatology, and Nutrition recommends that ESR and CRP have high specificity for organic disease, but lower sensitivity for inflammatory bowel disease (IBD) compared to fecal markers in patients with chronic diarrhea 1, 5
Total IgA levels should be checked when testing for celiac disease to identify potential IgA deficiency that could lead to false-negative results, as recommended by the American College of Gastroenterology 2, 6

Fecal calprotectin or fecal lactoferrin should be used to screen for inflammatory bowel disease (IBD) with a threshold value of 50 mg/g for calprotectin and 4.0-7.25 mg/g for lactoferrin to optimize sensitivity, as recommended by the American Gastroenterological Association 1
Giardia testing using antigen detection or polymerase chain reaction (PCR) is strongly recommended due to high prevalence and excellent test performance in patients with chronic diarrhea 1, 2

IgA tissue transglutaminase (tTG) antibody test with a second test to detect celiac disease in the setting of IgA deficiency should be used, as recommended by the American College of Gastroenterology 2
For IgA-deficient patients, IgG-tTG or tests for IgG deaminated gliadin peptides should be used to diagnose celiac disease, as recommended by the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition 2

Relying solely on ESR or CRP to screen for IBD when fecal calprotectin or lactoferrin are more sensitive markers, as warned by the American Gastroenterological Association 1, 5
Failing to check total IgA levels when testing for celiac disease, which could lead to false-negative results in IgA-deficient patients, as cautioned by the American College of Gastroenterology 2, 6