Plasma levels of S100A8/A9 and total white blood cell (WBC) counts were measured in 181 adults and children who presented to three emergency departments with right-sided or infraumbilical acute abdominal pain of less than 2 weeks' duration and no dysuria or recent trauma. The prevalence of acute appendicitis was 23%. For predicting acute appendicitis, S199A8/A9 (at a cutoff of 20 units) had a sensitivity of 93%, specificity of 54%, negative predictive value of 96%, and positive predictive value of 37%. Corresponding values for total WBC count (at a cutoff of 10 to the third power) were 62%, 67%, 86%, and 36%.
Comment: These preliminary data show promise for the S100A8/A9 test in patients with possible acute appendicitis, but the findings of this pilot study must be validated in a prospective trial. This study also shows, yet again, the futility of the outdated and discredited — but surprisingly persistent — practice of using WBC count to diagnose appendicitis.
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