Table 3 Summarises the diagnostic criteria of the different disease categories.

Disease category	Diagnostic criteria	References
RCD I	Villous atrophy persisted or recurred despite strict adherence to a gluten‐free diet. (assessed by a dietician and negative tTG antibodies)	2–4 8 19
	At least partial villous atrophy (Marsh IIIA) according to the modified Marsh criteria
	Excluding other causes of villous atrophy
	When ⩽10% aberrant T cells in intestinal biopsy
	IEL phenotype is normal with the expression of surface CD3, CD8 and TCR
RCD II	The same as RCD I, in addition to the presence of ⩾20% aberrant T cells in intestinal biopsy	2–4 8 19
	The IELs have normal morphology, but exhibit an aberrant phenotype (normal expression of CD103 and CD7, downregulation of surface CD3 to intracytoplasmic CD3, and the lack of surface T‐cell markers: CD4, CD8 and TCRs)
	EATL has been confidently excluded
Secondary EATL	WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues	45 46
	The patient is already known to have RCD
Primary (de novo) EATL	WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues	45 46
	No previous history of complicated coeliac disease
	Evidence of Marsh IIIA‐C in non‐involved mucosa

IEL, intraepithelial T lymphocyte; RCD, refractory coeliac disease; TCR, T‐cell receptor; tTG, tissue transglutaminase; WHO, World Health Organization.