What laboratory tests are used for the diagnosis and management of inflammatory bowel disease (IBD)?

Laboratory Tests for Inflammatory Bowel Disease

For patients with suspected or known IBD, obtain a complete blood count, C-reactive protein, erythrocyte sedimentation rate, serum electrolytes, liver enzymes, serum albumin, renal function, and fecal calprotectin, while mandatorily excluding infectious causes through stool cultures and Clostridium difficile toxin testing. 1

Core Laboratory Panel for IBD Assessment

Essential Blood Tests

• Complete blood count (CBC) including hemoglobin, leukocyte count, and platelet count to detect anemia, leukocytosis, and thrombocytosis that commonly accompany active disease 1
• Inflammatory markers: C-reactive protein (CRP) is superior to erythrocyte sedimentation rate (ESR) for evaluating acute disease activity, particularly in Crohn's disease where it correlates better with endoscopic findings 1
• Serum electrolytes to identify imbalances from diarrhea and malabsorption 1
• Liver enzymes to assess hepatobiliary involvement and monitor for medication-related toxicity 1
• Serum albumin and pre-albumin to evaluate nutritional status and degree of inflammation 1
• Renal function (creatinine and urea) to assess kidney status and guide medication dosing 1

Stool-Based Testing

• Fecal calprotectin is the most sensitive non-invasive marker for intestinal inflammation, useful for diagnosis, assessing disease severity, and monitoring treatment response 1
• Stool cultures to exclude bacterial pathogens 1
• Clostridium difficile toxin testing is mandatory in all suspected flares, as C. difficile infection is associated with higher mortality and increased healthcare utilization 1
• Cytomegalovirus testing should be performed when infectious causes are suspected during disease flares 1

Anemia Workup in IBD

Initial Assessment

• Hemoglobin thresholds: <13 g/dL for men, <12 g/dL for women, <11 g/dL for pregnant women and children 6 months to 5 years 1
• Red blood cell indices: Mean corpuscular volume (MCV) and red cell distribution width (RDW) to differentiate anemia types 1
• Reticulocyte count to assess bone marrow response 1

Iron Status Determination

• Serum ferritin <30 μg/L indicates iron deficiency in patients without active inflammation 1
• Serum ferritin up to 100 μg/L may still represent iron deficiency when inflammation is present 1
• **Transferrin saturation <20%** with ferritin >100 μg/L suggests anemia of chronic disease 1
• Ferritin 30-100 μg/L indicates mixed iron deficiency and anemia of chronic disease 1

Extended Anemia Panel

• Vitamin B12 and folic acid levels to identify macrocytic anemia, particularly in patients with extensive small bowel disease or ileal resection 1
• Haptoglobin and lactate dehydrogenase if hemolysis is suspected 1
• Soluble transferrin receptor for complex cases where iron status remains unclear 1

Diagnostic Considerations

Initial Diagnosis

Diagnosis requires a combination of clinical history, laboratory findings, endoscopic evaluation with biopsies, and exclusion of infectious causes—no single gold standard test exists. 1

• Laboratory abnormalities in active IBD typically include anemia, leukocytosis, thrombocytosis, elevated liver enzymes, hypoalbuminemia, and increased inflammatory markers 1
• Iron studies including serum iron, total iron-binding capacity, and transferrin saturation should be obtained at initial diagnosis 1
• Vitamin D level should be assessed at diagnosis 1
• Immunization status should be documented 1

Monitoring Frequency

• Stable outpatients: Complete blood count and CRP should be monitored regularly, though specific intervals depend on disease activity and treatment 1
• Patients with extensive small bowel resection or ileal disease: Vitamin B12 and folate should be assessed more frequently than annually 1
• During flares: Repeat infectious workup including C. difficile and consider cytomegalovirus testing 1

Important Caveats

CRP Limitations

• Normal CRP does not exclude active IBD, as some patients (particularly with ulcerative colitis) may have active disease without CRP elevation 1
• CRP correlates better with endoscopic activity in Crohn's disease than ulcerative colitis 1

Serologic Markers

• Perinuclear anti-neutrophil cytoplasmic antibodies (pANCA) and anti-Saccharomyces cerevisiae antibodies (ASCA) have limited sensitivity and are not recommended for routine diagnosis or therapeutic decisions 1, 2
• Serologic testing has only 60% sensitivity and 92% specificity for IBD diagnosis, inferior to the combination of anemia and elevated ESR (83% sensitivity, 96% specificity) 3

Fecal Calprotectin Specificity

• While highly sensitive for intestinal inflammation, fecal calprotectin lacks specificity to distinguish IBD from other causes of inflammation including infections and medication effects 1
• Home-based calprotectin testing provides reliable monitoring and enables eHealth approaches 1

Hospitalized Patients

• The recommended monitoring timelines do not apply to hospitalized patients, who require more frequent laboratory assessment based on clinical status 1
• Comprehensive metabolic panel, liver enzymes, and lipase should always be included for emergency room evaluations 1