Predictors of non-diagnostic ultrasound scanning in children with suspected appendicitis.

OBJECTIVE: To determine predictors of diagnostically inaccurate ultrasound scanning for suspected appendicitis. STUDY
DESIGN: Prospective emergency department cohort study of 263 previously healthy children 4 to 17 years of age undergoing ultrasound scanning. Ultrasound scanning results were interpreted as positive, negative, or equivocal for appendicitis and classified as diagnostically accurate and inaccurate. The main outcome measure was association between inaccurate ultrasound scanning and age, sex, body mass index percentiles, pain duration, white blood cell count, Faces Pain Score-Revised, clinical probability of appendicitis, and ultrasound scanning operator.
RESULTS: Of the 263 patients, 95 ultrasound scanning examinations were read as positive, 76 as negative, and 92 were equivocal. A total of 162 (61.6%) ultrasound scanning examinations were accurate (TP86, TN76), and 101 (38.4%) ultrasound scanning examinations were inaccurate (FP88, FN13). Children with body mass index percentiles ≥ 85 and clinical probability of appendicitis ≤ 50% had 58.1% probability of inaccurate ultrasound scanning examination (odds ratio, 2.48; 95% confidence interval, 1.48-2.78). In lean children, diagnostic accuracy of the screening ultrasound scanning examination with second ultrasound scanning or clinical reassessment was 93% versus 83% in the obese children (95% confidence interval of the difference, 1-19%).
CONCLUSION: Screening ultrasound scanning for pediatric appendicitis has suboptimal accuracy, particularly in obese children with a low likelihood of appendicitis who should not routinely undergo ultrasound scanning. However, when followed by a second ultrasound scanning or a clinical reassessment, it offers high diagnostic accuracy in lean children.