Inflammatory Bowel Disease Diagnosis

Biomarkers

• Fecal calprotectin is a validated stool biomarker for IBD diagnosis and monitoring, with a sensitivity of 93% and specificity of 96% for diagnosing IBD in adults, and a sensitivity of 92% and specificity of 76% in children and teenagers 1
• Fecal lactoferrin is another validated marker for IBD, helping to differentiate IBD from irritable bowel syndrome (IBS) or functional disease 1
• Fecal calprotectin levels can be categorized as follows:
• The following table summarizes biomarker thresholds, sensitivity, and specificity:

4, 2, 3, 5

• Elevated fecal calprotectin levels reliably differentiate IBD from IBS with specificity and sensitivity exceeding 85% 4
• Fecal lactoferrin is useful for monitoring response to therapy, with declining levels suggesting improving inflammation and persistently elevated levels indicating potential treatment failure 2

Diagnostic Procedures

• Endoscopy with biopsy remains the gold standard for IBD diagnosis, involving ileocolonoscopy examining the terminal ileum and all colonic segments, precise description of lesions, and biopsies from affected and non-affected areas 1, 6
• Upper GI endoscopy with biopsies is essential to evaluate for small bowel inflammation not detected on colonoscopy, and should include biopsies even from normal-appearing mucosa, with consideration of wireless capsule endoscopy or enteroscopy if upper endoscopy is non-diagnostic 7
• Colonoscopy with biopsies is necessary to evaluate for IBD and other causes of intestinal inflammation, with the AGA and the National Comprehensive Cancer Network strongly recommending endoscopy for patients with moderate-to-severe symptoms and a positive lactoferrin test 8, 2

Laboratory Tests

• C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are used as inflammatory markers 1, 9
• Complete blood count, including hemoglobin, leukocyte count, and platelet count, is used for anemia assessment and other purposes 9
• Biochemical tests, including serum electrolytes, liver enzymes, serum albumin, and renal function, are used to assess nutritional status and other factors 9
• Transferrin saturation (TfS) is used alongside ferritin to diagnose iron deficiency in IBD 10, 11

Iron Deficiency Assessment and Management

• Fecal calprotectin >150 μg/g is considered elevated and indicates ongoing intestinal inflammation despite normal colonoscopy findings, with the American Gastroenterological Association (AGA) recommending endoscopic assessment for patients with mild symptoms and elevated inflammatory markers 2
• The AGA recommends against empiric treatment adjustment without endoscopic assessment for patients with mild symptoms and elevated inflammatory markers, instead suggesting endoscopic evaluation to guide treatment decisions 2

Differential Diagnosis and Treatment

• Check for Clostridioides difficile and other enteric pathogens as potential causes of elevated calprotectin, with the Infectious Diseases Society of America (IDSA) recommending against using fecal leukocyte examination to establish the cause of acute infectious diarrhea (strong, moderate recommendation) 5, 2
• Consider segmental disease, as inflammatory bowel disease can present with patchy or segmental involvement that may be missed during routine colonoscopy, with diagnostic misclassification occurring in up to 10% of IBD diagnoses within the first 5 years after symptom onset 7
• Fecal leukocytes have limited diagnostic utility, with sensitivity of 28% for C. difficile and 36% for invasive bacterial pathogens, and stool cultures should be obtained for acute diarrhea with fever or bloody stools 12, 13
• The AGA recommends that treatment should be guided by the specific diagnosis established through endoscopy, with initiation of appropriate anti-inflammatory treatment based on disease type and severity, and avoiding empiric treatment without diagnosis 8, 2
• The IDSA recommends treating the underlying cause rather than the presence of leukocytes, and for C. difficile, discontinuing offending antibiotics and treating with appropriate antimicrobials is recommended 14
• Fluid and electrolyte replacement is recommended for all patients with significant diarrhea, with oral rehydration therapy as first-line for mild-moderate dehydration and intravenous fluids for severe dehydration or inability to tolerate oral intake 15, 13

Monitoring and Follow-up

• The AGA recommends monitoring fecal lactoferrin every 3-6 months to assess treatment response in patients with IBD, with serial monitoring of fecal calprotectin levels at 3-6 month intervals for confirmed IBD, targeting normalization of calprotectin as a treatment goal 8, 2, 3, 16, 17
• Elevated calprotectin in patients with quiescent IBD can predict clinical relapse with >85% sensitivity and specificity, and rising fecal lactoferrin levels may predict clinical flares 4, 2
• The IDSA recommends that follow-up testing is not recommended in most people following resolution of symptoms (strong, moderate recommendation), but clinical and laboratory reevaluation may be indicated for persistent symptoms 5