Table 2. Sensitivity, specificity, and positive and negative predictive values of penicillinase tests using blaZ PCR as the standard.

Penicillinase test	Sensitivity (%)	Specificity (%)	Positive predictive value (%)	Negative predictive value (%)
Nitrocefin-based test	50	99.5	50	99.5
P2 zone diameter interpretation*	100	96.5	22.2	100
P2 zone edge test	100	99	50	100
P10 zone diameter interpretation†	50	100	100	99.5
P10 zone edge test	100	95.5	18.2	100
Cloverleaf test	50	100	100	99.5

^*P2 zone diameters were interpreted according to the EUCAST criteria (isolates with a P1 diameter of ≤25 mm were considered resistant) [11]; ^†P10 zone diameters were interpreted according to the CLSI criteria (isolates with a P10 diameter of ≤28 mm were considered resistant) [11].