Diagnostic accuracy of laboratory and ultrasound findings in patients with a non-visualized appendix

Abstract

Ultrasound (US) and laboratory testing are initial diagnostic tests for acute appendicitis. A diagnostic dilemma develops when the appendix is not visualized on US. Objective: To determine if specific US findings and/or laboratory results predict acute appendicitis when the appendix is not visualized. Methods: A prospective study was conducted on children (birth-18 yrs) presenting to the pediatric emergency department with suspected acute appendicitis who underwent right lower quadrant US.Children with previous appendectomy, US at another facility, or eloped were excluded. US findings analyzed: inflammatory changes, right lower quadrant and lower abdominal fluid, tenderness during US exam and lymph nodes. Diagnoses were confirmed via surgical pathology. Results 1252 subjects were enrolled, 60.8% (762) had appendix visualized and 39.1% (490) did not. In children where the appendix was not seen, 6.7% [33] were diagnosed with appendicitis. Among patients with a non-visualized appendix, the likelihood of appendicitis was significantly greater if: inflammatory changes in the RLQ (OR 18.0, 95% CI 4.5–72.1), CRP >0.5 mg/dL (OR 2.64, 95% CI 1.0–6.8), or WBC > 10 (OR 4.36, 95% CI 1.66–11.58). Duration of abdominal pain >3 days was significantly less likely associated with appendicitis in this model (OR 0.34, 95% CI 0.003–0.395). Combined, the absence inflammatory changes, CRP < 0.5 mg/dL, WBC < 10, and pain, ≤3 days had a NPV of 94.0%. Conclusion When the appendix is not visualized on US, predictors for appendicitis include the presence of inflammatory changes in the RLQ, an elevated WBC/CRP and abdominal pain <3 days.