Table 4  Performance metrics of 4C Mortality Score to rule out and rule in mortality at different cut-off values in validation cohort
Cut-off value  No of patients (%)  TP  TN  FP  FN  Sensitivity (%)  Specificity (%)  PPV (%)  NPV (%)  Mortality (%)
Rule out mortality
≤2  1001 (4.5)  6724  996  14 636  5  99.9  6.4  31.5  99.5  0.5
≤3  1650 (7.4)  6709  1630  14 002  20  99.7  10.4  32.4  98.8  1.2
≤4  2420 (10.8)  6672  2363  13 269  57  99.2  15.1  33.5  97.6  2.4
≤6  4121 (18.4)  6542  3934  11 698  187  97.2  25.2  35.9  95.5  4.5
≤8  6539 (29.2)  6223  6033  9599  506  92.5  38.6  39.3  92.3  7.7
≤9  8167 (36.5)  5911  7349  8283  818  87.8  47  41.6  90.0  10.0
Rule in mortality
≥9  15 822 (70.8)  6223  6033  9599  506  92.5  38.6  39.3  92.3  39.3
≥11  12 325 (55.1)  5483  8790  6842  1246  81.5  56.2  44.5  87.6  44.5
≥13  8069 (36.1)  4206  11 769  3863  2523  62.5  75.3  52.1  82.3  52.1
≥15  4158 (18.6)  2557  14 031  1601  4172  38  89.8  61.5  77.1  61.5
≥17  1579 (7.1)  1142  15 195  437  5587  17  97.2  72.3  73.1  72.3
≥19  381 (1.7)  305  15 556  76  6424  4.5  99.5  80.1  70.8  80.1
FN=false negative; FP=false positive; NPV=i negative predictive value; PPV=positive predictive value; TN=true negative; TP=true positive.