Table 4.

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

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%)

AA, Acute appendicitis, AAS, Adult Appendicitis Score