Six studies, with a total of 671 participants, were included in the review. All ultrasonography and computed tomography (CT) results were assessed independently from one another and from the reference standard. However, the reference standard was not assessed independently of the index test results. The time between ultrasonography and CT was not reported in two studies and was three hours or less in all other studies.

__Diagnostic value of computed tomography (CT)__: The summary estimates for the sensitivity CT in diagnosing appendicitis was 0.91 (95% CI 0.84 to 0.95) and for specificity was 0.90 (95% CI 0.85 to 0.94). The summary estimate of the positive likelihood for CT was 9.29 (95% CI 6.86 to 12.6) and for the negative likelihood ratio was 0.10 (95% CI 0.06 to 0.17).

__Diagnostic value of graded compression ultrasonography__: The summary estimate for the sensitivity of ultrasonography was 0.78 (95% CI 0.67 to 0.86) and for specificity was 0.83 (95% CI 0.76 to 0.88). The summary estimate of the positive likelihood for ultrasonography was 4.5 (95% CI 3.03 to 6.68) and for the negative likelihood ratio was 0.27 (95% CI 0.17 to 0.43).

Summary sensitivity (p<0.017), specificity (p<0.037), positive likelihood (p=0.011) and negative likelihood (p=0.013) values differed significantly between CT and ultrasonography, in favour of CT.

Overall post-test probabilities, following a positive test, were 90% for CT and 82% for ultrasonography. Overall pos-test probabilities, following a negative test, were 9% for CT and 21% for ultrasonography. CT showed significantly better diagnostic performance at every clinically relevant prevalence. Post-test probabilities, following a positive test, decreased with lower prevalence.