99mTc-hexamethylpropyleneamine oxime (Tc-WBC) scan for diagnosing acute appendicitis in children

We used a radiolabeled white blood cell (WBC) scan as an adjunct to diagnose appendicitis in 100 children with equivocal signs or symptoms of appendicitis. WBC separation and labeling took 2 hours. Patients were imaged up to 3 hours after injection of labeled Tc-WBC. Accuracy was established in all 100 children by histopathological findings, medical records and follow-up interviews. Scans were positive in 40 and negative in 60. Positive scans averaged 76 +/- 40 minutes after injection (mean +/- SD); negative scans required 150-180 minutes. Tc-WBC scan correctly identified appendicitis in 36 of 37 children (sensitivity, 97%) and correctly excluded appendicitis in 59 of 63 (specificity, 94%). The false negative scan occurred in a patient whose perforated appendix was discovered at operation 3 days following the scan. Accuracy of the examination was 95 per cent, with a positive predictive value of 90 per cent and a negative predictive value of 98 per cent. The negative laparotomy rate for the entire group was 4 per cent. Tc-WBC imaging is an accurate, noninvasive test for ruling out appendicitis in children with right lower quadrant abdominal pain and equivocal presentation, although positive scans require more clinical judgment. The high sensitivity and negative predictive value suggest its potential for screening and discharging children from the emergency department.