Effect of Alvarado Score on the Negative Predictive Value of Nondiagnostic Ultrasound for Acute Appendicitis

BACKGROUND: The purposes of this study were to calculate the negative predictive value (NPV) of nondiagnostic ultrasound (US) in patients with suspected appendicitis and to identify the clinical factors that were associated with the nondiagnostic US. METHODS: We conducted a retrospective review of 412 patients who had graded-compression appendiceal US performed during January 2017 and December 2017. The NPV of the nondiagnostic US in combination with clinical parameters was calculated. Multivariate regression analysis was used to determine the independent predictors for the nondiagnostic US. RESULTS: The US exam was nondiagnostic in 64.8% of the patients, giving an NPV of 70.8%. The NPV of nondiagnostic US increased to 96.2% in patients who had an Alvarado score of <5. The patients who did not have migratory pain, did not have leukocytosis, and had a pain score of <7 were more likely to have a nondiagnostic US study (P < 0.001). CONCLUSION: Alvarado score had an inverse effect on the NPV of nondiagnostic appendiceal US. Patients who had nondiagnostic US and Alvarado score of <5 were very unlikely to have appendicitis. Active clinical observation or re-evaluation rather than immediate computed tomography may be a safe alternative approach in these low-risk patients. However, the Alvarado score itself was not a predictive factor of nondiagnostic US. The absence of migratory pain, absence of leukocytosis, and low pain score were the independent predictors of nondiagnostic appendiceal US.