Definitions of response and remission for the Robarts Histopathology Index

The Robarts Histopathology Index (RHI) is a recently validated instrument that measures histological disease activity in ulcerative colitis.1 Given the increasing importance and use of histology in UC as a treatment outcome, additional evaluation and clarification of the definitions for histological remission and response using the RHI is needed.

During the development of the RHI, we demonstrated that most patients in clinical or endoscopic remission had an RHI≤6. However, an RHI≤6 should not be used to define histological remission as was recently suggested by Magro et al.2 Rather, the minimal criteria for histological remission should be the absence of neutrophils from the mucosa (both lamina propria and epithelium), as neutrophils have long been used to define histologically active disease.3 Furthermore, the presence of mucosal neutrophils in biopsies from patients in clinical remission predicts clinical relapse.4 Using the RHI, an absence of mucosal neutrophils is...

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