Background and Aims: Patient-reported outcome measures [PROMs] aim to measure patients perception of how their disorder influences everyday functioning. The objective of this study was to develop a PROM to assess disease activity in microscopic colitis [MC] fulfilling the requirements of the Food and Drug Administration [FDA].

Methods: The European Microscopic Colitis Activity Index [E-MCAT] was developed in four steps. [1] A list of symptoms associated with active MC was created by a group of experts in the field. [2] Content validity of the symptoms was performed by experts [n= 14] and patients [n = 79] using the Content Validity Index. [3] Questions and response alternatives were created for each symptom, and validity of the E-MCAI was evaluated with cognitive interviews with patients [n= 7] and by the experts. [4] A pilot postal survey was performed to ensure usability.

Results: Seven of the symptoms related to active MC fulfilled the criteria for content validity and were included in the E-MCAI: stool consistency, stool frequency, stools at night, feel a need to pass more stools shortly after a bowel movement, urgent need to empty the bowel, leakage of stool and abdominal pain.The development and validation process resulted in the current version of the E-MCAI consisting of six questions related to MC. Conclusions: The E-MCAI was developed using the methods advocated by the FDA.The evaluation indicates good content validity. Further evaluation will be performed to achieve construct validity, reliability and responsiveness in future cross-sectional and longitudinal studies.