Diagnostics of Colitis Microscopica

Biopsy Locations and Standards

The European Society of Gastrointestinal Endoscopy recommends taking biopsies from the right colon (ascending and transverse) and left colon (descending and sigmoid), with a minimum of 2 samples from each segment, placed in separate containers 1, 2, 3
Biopsies from the rectum must be taken from all patients with unexplained diarrhea, as this is the minimum standard, unless there are contraindications 1, 2, 3
Biopsies from the right and left sides of the colon should be taken from 100% of patients undergoing colonoscopy for unexplained diarrhea, as colitis microscopica can be focal 1, 2, 3

The rectum has the lowest diagnostic value (82.2%), so biopsies only from the rectum may give a false negative result in 34-43% of cases 4, 5
Biopsies from the ascending colon have the highest diagnostic value (96.9%), followed by the transverse colon (95.7%) and the descending colon (85.0%) 4, 5

If sigmoidoscopy is performed instead of colonoscopy, it is necessary to take biopsies from the descending colon in addition to the rectum and sigmoid colon 6
Biopsies only from the rectum and sigmoid colon may not reveal the disease in some cases 6
Biopsies should also be taken from macroscopically normal mucosa, as a macroscopically normal examination does not exclude all causes of unexplained diarrhea 1, 2, 3