Fig. 2

The quality evaluations of included studies through QUADAS-2. The risk of bias was low in most of the studies. Among them, the number of studies having a high risk of bias was two, two, zero and three in the domains of flow and timing, reference standard, index test(s), and patent selection, respectively. The majority of studies were of good applicability. Only one studies presented great concerns in the reference standard domain and one in the patient selection domain