From https://associationofanaesthetists-publications.onlinelibrar...
Due to the associated time and costs, some health officials propose the elimination of fit testing and advocate that a fit check is sufficient in determining respirator fit [39]. The NIOSH conducted a study that demonstrated protection of N95/FFP2 masks improved from 67% without fit testing to 96% with fit testing [40]. Subsequently, NIOSH determined fit check alone to be insufficient and fit testing should be mandatory when selecting filtering facepiece respirators or elastomer half mask respirators.
Three studies that included 1111 Asians assessed the ability of fit check to detect leak determined by a quantitative fit test [36, 41, 42]. Average (range) sensitivity and specificity of the fit check to correctly detect leak were 26 (14–40)% and 79 (58–92)%, respectively, and consequent average (range) fit test pass rate following ‘successful’ fit check was 56 (34–73)%. Another study found the protection factor of filtering facepiece respirators increased from 3.3 to 20.5 when comparing the results of the entire test panel with those who had passed the fit test [32]. However, non‐fitted filtering facepiece respirators are still likely to provide greater protection than surgical masks, with a measured protection factor of 1.2 (Table 1) [32].
In summary, while fit check remains recommended before each use of any respirator to ensure fit on a day‐to‐day basis (Grade 1C evidence), we recommend not to use fit check as a substitute for fit testing to identify the size and shape of respirator that fits best (Grade 1B evidence).