What lab tests and treatments are recommended for a Crohn's (Crohn's disease) flare-up?

Laboratory Tests for Crohn's Disease Flare-Up

For a suspected Crohn's disease flare-up, obtain a complete blood count, C-reactive protein, erythrocyte sedimentation rate, comprehensive metabolic panel including liver enzymes and albumin, renal function tests, and fecal calprotectin, while mandatorily excluding infectious causes with stool cultures and Clostridium difficile toxin testing. 1

Essential Laboratory Panel

Mandatory Blood Tests

• Complete blood count with differential to assess for anemia (common in active disease), leukocytosis, and thrombocytosis 1
• C-reactive protein (CRP) - the preferred inflammatory marker as it is more sensitive than ESR and correlates better with endoscopic disease activity in Crohn's disease 1
• Erythrocyte sedimentation rate (ESR) - though less sensitive than CRP, it provides complementary inflammatory assessment 1
• Serum albumin and pre-albumin to assess nutritional status and degree of inflammation 1
• Comprehensive metabolic panel including electrolytes, liver enzymes, and renal function 1
• Iron studies to evaluate for iron deficiency anemia 1

Stool Studies (Mandatory)

• Fecal calprotectin - correlates better with endoscopic inflammation than CRP or white blood cell count 1
• Stool cultures to exclude bacterial pathogens 1
• Clostridium difficile toxin test - mandatory to rule out infectious triggers, as C. difficile can precipitate or mimic flares 1
• Cytomegalovirus testing should be considered in suspected flares, particularly in severe cases 1

Interpretation of Key Biomarkers

Fecal Calprotectin Cutoffs

• <150 mg/g effectively rules out active inflammation in asymptomatic patients (sensitivity 81%, specificity 72%) 1
• >250 mg/g suggests endoscopically active disease, though confirmation with endoscopy is recommended before treatment escalation 1
• Fecal calprotectin is particularly useful as it correlates better with mucosal inflammation than serum markers 1

C-Reactive Protein

• CRP >5 mg/L in symptomatic patients with moderate to severe symptoms suggests endoscopic activity and may preclude routine endoscopic assessment 1
• Normal CRP (<5 mg/L) in asymptomatic patients helps rule out active inflammation 1
• Note that CRP may be normal in some patients with active Crohn's disease, particularly isolated ileal disease 1

Clinical Context and Pitfalls

Important Caveats

• Biomarkers alone are insufficient in mildly symptomatic patients - neither normal nor elevated biomarkers accurately determine endoscopic activity in this setting 1
• Discordance between symptoms and biomarkers merits endoscopic evaluation for confirmation 1
• CRP correlates better with endoscopic disease activity in Crohn's disease than in ulcerative colitis 1
• Therapies may cause abnormalities in liver enzymes, leukocytes, and kidney function, so baseline medication effects must be considered 1

Disease Activity Assessment

• Laboratory findings in active disease typically include anemia, leukocytosis, thrombocytosis, elevated liver enzymes, hypoalbuminemia, and increased inflammatory markers 1
• The combination of elevated CRP and fecal calprotectin provides the most reliable assessment of inflammatory activity 1
• Hemoglobin, hematocrit, and platelet count show statistical significance in correlating with disease activity 2

Monitoring Strategy

A biomarker- and symptom-based monitoring strategy is superior to symptoms alone for patients in symptomatic remission 1. The 2023 AGA guidelines recommend:

• In asymptomatic patients: fecal calprotectin <150 mg/g and normal CRP reliably rule out active inflammation, avoiding unnecessary endoscopy 1
• In symptomatic patients with moderate to severe symptoms: elevated fecal calprotectin or CRP suggests endoscopic activity 1
• Regular monitoring every 3-12 months as part of global disease assessment includes complete blood count, liver profile, albumin, iron studies, renal function, CRP, and fecal calprotectin 1