What are the differential diagnoses for an adult patient with elevated CRP (C-Reactive Protein), elevated WBC (White Blood Cell) count, and chronic gastrointestinal blood loss in the absence of anemia?

Differential Diagnoses for Elevated CRP, Elevated WBC, and Chronic GI Blood Loss Without Anemia

The most critical differentials to consider are inflammatory bowel disease (particularly Crohn's disease or ulcerative colitis), gastrointestinal malignancy, and celiac disease, with IBD being the most likely given the combination of inflammatory markers and chronic blood loss. 1

Primary Differential Diagnoses

Inflammatory Bowel Disease (IBD)

• Crohn's disease and ulcerative colitis are the leading considerations when elevated inflammatory markers (CRP and WBC) accompany chronic GI blood loss 1
• CRP correlates with disease activity in IBD, though it may be normal in some patients with active ulcerative colitis 1
• Elevated WBC count and CRP together suggest active intestinal inflammation requiring endoscopic evaluation 1
• The absence of anemia does not exclude IBD, as blood loss may be compensated or intermittent 1
• Fecal calprotectin >250 μg/g would strongly support IBD diagnosis and warrant urgent gastroenterology referral 1

Gastrointestinal Malignancy

• Colorectal cancer must be excluded in any adult with chronic GI blood loss, particularly if age >40 years 1, 2
• Gastric cancer can present with occult bleeding and elevated inflammatory markers 2
• Elevated CRP and WBC may reflect tumor-associated inflammation rather than infection 1, 3
• Even without anemia, malignancy remains a critical diagnosis requiring colonoscopy and upper endoscopy 1, 2

Celiac Disease

• Celiac disease causes chronic GI blood loss through mucosal inflammation and malabsorption 1
• Can present with elevated inflammatory markers without overt GI symptoms 1, 2
• Testing for tissue transglutaminase IgA and total IgA is reasonable in patients with chronic GI symptoms and elevated inflammatory markers 1
• Small bowel biopsy during upper endoscopy is diagnostic 1, 2

Secondary Differential Diagnoses

Infectious Etiologies

• Clostridioides difficile must be excluded before initiating immunosuppression if IBD is suspected 1
• Chronic parasitic infections (particularly in endemic areas) can cause persistent inflammation and occult bleeding 1
• Helicobacter pylori gastritis may cause chronic blood loss with inflammatory response 2

Vascular Lesions

• Colonic vascular ectasia (angiodysplasia) causes chronic occult bleeding 2
• These lesions typically occur in older patients and may not elevate inflammatory markers significantly 2

Peptic Ulcer Disease

• Chronic peptic ulcers can cause occult bleeding with inflammatory response 2
• NSAID use is a critical historical factor to assess 1

Anemia of Chronic Disease (Without Frank Anemia Yet)

• Elevated CRP and WBC suggest underlying chronic inflammation that may eventually lead to anemia 3
• Hepcidin upregulation in chronic inflammation can cause functional iron deficiency before anemia develops 1, 3

Diagnostic Approach Algorithm

Initial Laboratory Assessment

• Complete blood count with differential, CRP, ferritin, iron studies, and transferrin saturation 1
• Fecal calprotectin (>100 μg/g suggests organic disease; >250 μg/g strongly suggests IBD) 1
• Tissue transglutaminase IgA and total IgA for celiac screening 1
• Stool studies including C. difficile toxin and culture 1

Endoscopic Evaluation

• Both upper endoscopy with small bowel biopsies and colonoscopy are mandatory to exclude malignancy and identify inflammatory or structural lesions 1, 2
• Endoscopy should not be delayed in patients with elevated inflammatory markers and chronic blood loss 1

Critical Clinical Pitfalls

• Do not assume normal hemoglobin excludes significant GI pathology—chronic blood loss may be compensated by increased erythropoiesis 1, 2
• CRP and WBC are non-specific markers; elevated values require definitive investigation rather than empiric treatment 1, 4
• Fecal calprotectin has superior specificity for intestinal inflammation compared to serum markers and should be obtained when IBD is suspected 1
• Never initiate immunosuppression without excluding infectious causes, particularly C. difficile 1
• The combination of elevated inflammatory markers with GI blood loss warrants aggressive investigation regardless of hemoglobin level 1