99Tcm-HMPAO-labelled white blood cell scans to detect acute appendicitis in older patients with an atypical clinical presentation.

Forty-nine patients (age > 50 years) with an acute abdomen and suspected appendicitis, but with atypical findings, were included in the study. After the intravenous injection of 99Tcm-hexamethylpropylene amine oxime (99Tcm-HMPAO) labelled white blood cells (WBCs), serial anterior images of the abdomen and pelvis were obtained after 30, 60, 120 and 240 min. Any abnormal localization of WBC accumulation in the right lower quadrant of the abdomen equal to or greater than bone marrow activity was considered positive. Twenty-five patients had positive WBC scans, all of whom underwent laparotomy. Twenty-three of these patients were shown to have appendicitis; the other 2 did not. The other 24 patients had a negative WBC scan, 2 of whom underwent laparotomy and were shown to have appendicitis; the other 22 patients did not undergo surgery and showed no evidence of appendicitis during follow-up. The overall sensitivity, specificity, accuracy, positive and negative predictive values of WBC scans for diagnosing appendicitis were as follows: 92.0%, 91.7%, 91.8%, 92.0% and 91.7% respectively. In conclusion, 99Tcm-HMPAO-labelled WBC scans provide a rapid and highly accurate method for diagnosing appendicitis in older patients with equivocal clinical findings.