Evaluating the optimum number of biopsies to assess histological inflammation in ulcerative colitis: a retrospective cohort study

Background: The optimal ulcerative colitis biopsy protocol is unclear. Aim: To evaluate the number of biopsies required to accurately assess microscopic disease activity in ulcerative colitis. Methods: Biopsies from patients with ≥4 rectosigmoid samples, and clinical and endoscopic data, were retrospectively obtained from a prospective biobank. Histology and endoscopic videos were read blindly. A 4-biopsy Robarts Histopathology Index (RHI) reference score, consisting of the worst item-level ratings from four biopsies, was compared to 1-, 2- and 3-biopsy estimates. Agreement was determined using bivariate errors-in-variable regression analysis (acceptance interval: ±8.25). Endoscopic activity and disease location subgroup analyses were also performed. Results: Forty-six patients had ≥4 rectosigmoid biopsies available (N = 287). The 2-biopsy (tolerance interval: −7.66, 4.79) and 3-biopsy (tolerance interval: −4.86, 3.46) RHI scores demonstrated acceptable agreement with 4-biopsy scores. One-biopsy scores demonstrated unacceptable agreement (tolerance interval: −13.99, 7.78). Mean RHI scores using the 2-, 3- and 4-biopsy approaches were similar (6.1 ± 9.6 P = 0.36; 6.8 ± 10.5, P = 0.7; 7.5 ± 11.2), whereas the 1-biopsy estimate was lower (4.4 ± 8.1, P = 0.06). Histological remission rates were identical for the 2-, 3- and 4-biopsy methods (65.2%, P = 1.0). Subgroup analysis demonstrated that three biopsies were required in patients with endoscopically active disease. Sampling additional colonic locations yielded lower histological remission rates compared to rectosigmoid sampling alone (33.3% vs 61.9%, P = 0.1). Conclusions: A minimum of two — conservatively, three — biopsies are required to reliably assess disease activity in a single colonic segment using the RHI. Further studies are needed of endoscopically active patients and sampling locations. These results have implications for biopsy strategies in clinical trials and practice.