Table 3.

Definitions of relapse in each study included.

Study	Disease Type	Definition of Relapse
A. Jauregui-Amezaga 2014 [47]	UC	Presence of blood in stool and MES ≥ 3 with histologic confirmation.
Buisson 2019 [62]	UC	Reappearance of clinical manifestation (SCCAI > 2 with subscore > 1 for at least one item among stool frequency and rectal bleeding) leading to medication intensification, hospitalization, or colectomy.
	CD	Reappearance of clinical manifestation (HBI > 4) leading to therapeutic intensification, hospitalization, or CD-related surgery.
F.Costa 2005 [54]	UC	Worsening of symptoms, accompanied by an increase in the UCAI score to >4, sufficient to require a change in therapy (addition of steroids, immunosuppressors, surgery, etc.).
	CD	Worsening of symptoms, accompanied by an increase in the CDAI score to >150, sufficient to require a change in therapy (addition of steroids, immunosuppressors, surgery, etc.).
D. Naismith 2014 [40]	CD	An unplanned escalation in therapy, progression of disease phenotype by the Montreal classification or hospitalisation and/or emergency surgery for active CD.
D’Inca 2008 [55]	UC	ET scores exceeding 4 and requiring additional treatment.
	CD	CDAI exceeding 150, with an increment of more than 50 points over the baseline score (75 points in resected patients) and requiring additional treatment.
Ferreiro-Iglesias 2018 [56]	UC	PMS > 2.
	CD	HBI > 4.
Gisbert 2009 [57]	UC	Truelove modified index > 11 points.
	CD	CDAI > 150.
Hosseini 2015 [48]	UC	Elevated Seo activity index higher than 220 or worsening of symptoms (including abdominal pain, diarrhea with or without blood and rectal bleeding) sufficient to require a change in therapy (increasing the dose, changing the current drug (s), addition of steroids, hospitalization or surgery).
Kallel 2010 [41]	CD	CDAI > 150 or an increase of more than 100 from the inclusion value and was sufficiently severe to warrant treatment.
Keshteli 2017 [49]	UC	PMS ≥ 3.
Kostas 2017 [58]	UC	(1) Significant increase in respective clinical activity indices above accepted cut-offs for remission in UC (Simple Colitis Activity Index ≥ 3) and/or (2) step up in the patient’s therapeutic regimen, including surgery for intractable disease-related symptoms.
	CD	(1) Significant increase in respective clinical activity indices above accepted cut-offs for remission in CD (HBI ≥ 5) and/or (2) step up in the patient’s therapeutic regimen, including surgery for intractable disease-related symptoms.
L. Ye 2017 [42]	CD	Worsening symptoms requiring intensified therapy or surgery or a CDAI score > 150, with confirmation by ileocolonoscopy.
Ferreiro-Iglesias 2016 [43]	UC	PMS > 3.
	CD	HBI > 4.
R.Ferreiro-Iglesias 2016 [59]	CD	HBI > 4.
S. MONTEIR 2019 [44]	CD	An unexpected escalation in therapy, hospitalization or surgery for active CD with ileocolonoscopy and inflammatory activity assessed by SES-CD or Rutgeerts score.
Shimoyama 2018 [50]	UC	The sum of ‘stool frequency’ score (0–3) and ‘rectal bleeding’ score (0–3) in the Mayo scoring system exceeding 0.
Theede 2017 [51]	UC	The symptoms of active UC demanding adjustment of actual or initiation of new UC therapy.
Tibble 2000 [7]	UC	HBI > 4 and an increase of >2 from the inclusion value. All relapses were of sufficient severity to warrant a change in treatment.
	CD	CDAI > 150 with an increase of >100 from the inclusion value. All relapses were of sufficient severity to warrant a change in treatment.
V. García-Sánchez 2009 [60]	UC	Worsening of the symptoms, accompanied by or a modified TW score of ≥11 points.
	CD	Worsening of the symptoms, accompanied by a CDAI score of ≥150 points.
Y. Zhulina 2016 [61]	IBD	Increasing symptoms necessitating intensified medical therapy or surgery.
Yamamoto 2013 [45]	CD	CDAI > 150 with an increase of ≥70 points.
Yamamoto 2014 [52]	UC	Worsening of stool frequency and/or rectal bleeding with an endoscopic score of 2 or 3.
Yamamoto 2018 [53]	UC	Worsening of stool frequency and/or rectal bleeding with the MES of 2 or 3.
D. Laharie 2011 [46]	CD	Increasing symptoms (CDAI > 250 within 2 weeks or CDAI > 150 with an at least 70 points of increase as compared with CDAI at week 14) or the need for an additional steroid or IFX course or for a surgical resection.

HBI: Harvey-Bradshaw index; PMS: partial Mayo score; MES: Mayo endoscopic score; UCAI: ulcerative colitis activity index; CDAI: Crohn’s disease activity index; ET score: Edwards and Truelove (ET) scores; SCAI: Simple Colitis Activity Index; SES-CD: Simple Endoscopic Score for Crohn Disease; and IFX: Infliximab.