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Table 4 Pre- and post-test probabilities of appendicitis, patients who underwent US or CT

From: Performance of imaging studies in patients with suspected appendicitis after stratification with adult appendicitis score

Probability of AA according to AAS Pre-test probability of AA Post-test probability of AA, positive test Post-test probability of AA, negative test
US
 All patients, n = 497 177/497 (37%) 86/104 (83%) 91/393 (23%)
 High, n = 52 41/52 (75%) 19/20 (95%) 22/32 (69%)
 Intermediate, n = 258 122/258 (47%) 59/65 (91%) 63/193 (33%)
 Low, n = 187 17/187 (9%) 8/19 (42%) 9/168 (5.4%)
CT
 All patients, n = 489 257/489 (53%) 253/260 (97%) 4/229 (1.8%)
 High, n = 114 90/114 (79%) 90/91 (99%) 0/23 (0%)
 Intermediate, n = 276 138/276 (50%) 135/148 (91%) 3/128 (2.3%)
 Low, n = 99 16/99 (16%) 15/20 (75%) 1/79 (1.3%)
  1. AA, Acute appendicitis, AAS, Adult Appendicitis Score