Next Step in Workup
This patient requires colonoscopy with biopsies to evaluate for inflammatory bowel disease (IBD), given the significantly elevated fecal calprotectin of 327 μg/g in the setting of bloody diarrhea with mucus, despite negative infectious workup. 1
Rationale for Colonoscopy
Fecal calprotectin >250 μg/g indicates high suspicion for IBD and warrants direct progression to colonoscopy without repeat testing, as this level has 88% sensitivity and 73% specificity for detecting endoscopic inflammation. 1, 2, 3
The combination of bloody diarrhea with mucus, abdominal pain, and elevated calprotectin strongly suggests organic intestinal inflammation rather than functional disease, making endoscopic evaluation mandatory. 1, 4
At age 59, this patient falls into the elderly-onset IBD category where up to 15% of new IBD diagnoses occur, but differential diagnosis must also include colorectal cancer, ischemic colitis, segmental colitis associated with diverticulosis, and microscopic colitis—all requiring tissue diagnosis. 1
Specific Colonoscopy Protocol
Complete ileocolonoscopy should be performed with systematic biopsies from at least six segments: terminal ileum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum, with a minimum of two biopsies per segment even from normal-appearing mucosa. 1
Targeted biopsies should be obtained from areas of inflammation, ulceration, or any suspicious lesions and placed in separately labeled containers. 1
The endoscopist must document the extent and severity of inflammation using validated scoring systems to establish baseline disease activity. 1
Additional Pre-Endoscopy Considerations
Repeat stool testing for Clostridioides difficile is mandatory before colonoscopy, as this infection can coexist with or mimic IBD, particularly in this age group. 1
Consider cytomegalovirus (CMV) testing if the patient has any immunosuppression history or if severe colitis is found at endoscopy. 1
Cross-sectional imaging with CT enterography or MR enterography should be considered if small bowel Crohn's disease is suspected based on clinical features, though colonoscopy remains the priority. 1
Why Other Tests Are Insufficient
The negative CRP does not exclude IBD, as CRP has only 49% sensitivity for detecting endoscopic activity and correlates better with Crohn's disease than ulcerative colitis. 1, 3
Repeating fecal calprotectin is unnecessary at this level (327 μg/g), as values >250 μg/g already indicate high probability of organic disease requiring endoscopic confirmation. 1
Stool lactoferrin would add no additional diagnostic value beyond the already elevated calprotectin. 3
Critical Pitfalls to Avoid
Do not delay colonoscopy to trial empiric therapy, as this patient's presentation with bloody diarrhea and elevated calprotectin mandates tissue diagnosis to exclude malignancy and establish the specific type of colitis. 1
Do not assume IBS-D based on the negative CRP alone, as fecal calprotectin is far more sensitive (88% vs 49%) for detecting mucosal inflammation. 3, 5
In elderly patients with left-sided segmental colitis and diverticulosis at endoscopy, consider both segmental colitis associated with diverticulosis and Crohn's disease in the differential, as these require different management strategies. 1