Table 2

Results of the QUADAS-2 quality assessment of included studies

Study	Risk of bias			Applicability concerns
	Patient selection	Index test	Reference standard	Flow and timing	Patient selection	Index test	Reference standard
Zacharaki EI 2009	+	–	+	+	+	?	+
Ryu 20148	+	+	?	+	+	?	+
Skogen 201612	+	+	+	+	+	–	?
Li-Chun Hsieh 201713	+	+	–	+	+	+	?
Ditmer 201815	+	?	+	+	+	?	+
Wang 201814	+	+	+	+	+	–	+

+: Low risk; -: High risk; ?: Unclear risk.
QUADAS, Quality Assessment of Diagnostic Accuracy Studies.