Lower WBC count associated with negative appendectomy

Image: PD

1. Withholding appendectomy for pediatric patients with white blood cell counts below 9000 and 8000 per uL increased the sensitivity of appendicitis detection to 92% and 95%, respectively.

Evidence Rating Level: 2 (Good)

Study Rundown: Appendicitis is a common surgical emergency among pediatric patients and can often be diagnosed based on clinical presentation. However, the potentially significant morbidity and mortality of perforation often results in surgical appendectomy before definitive diagnosis. No single test or algorithm has been found to be reliable for diagnosing appendicitis leaving most healthcare providers to rely on clinical suspicion combined with imaging techniques.  Researchers in the current study sought to determine predictors for negative appendectomies (NA) by reviewing laboratory studies and radiographic findings among all children who underwent surgery for suspected appendicitis at a tertiary children’s hospital from 2009 to 2012. The authors used white blood cell (WBC) count data from those with NA and with true appendicitis in their evaluation of the sensitivity and specificity of WBC as a test for appendicitis. WBC counts were found to be lower among patients with NA, normal appendices upon appendectomy. The authors concluded that utilizing a lower WBC count than the 11500 per uL specified in previous scoring methods such as the Alvarado (or MANTRELS) score will improve diagnostic accuracy. While this study is limited in its generalizability as it only included patients treated at a single hospital, lowering the WBC count criterion in appendicitis clinical decision-making tools has the potential to reduce unnecessary appendectomies.

Click to read the study in Pediatrics

Relevant Reading: A practical score for the early diagnosis of acute appendicitis

In-Depth [retrospective cohort]: This study evaluated 847 children who underwent an open or laparoscopic appendectomy for presumed appendicitis from 2009 to 2012. Twenty-two of these patients were found to have a pathologically normal appendix (NA).  WBC counts were obtained for all patients who underwent appendectomy, with an elevated WBC count defined as >11 500 per uL. A normal WBC count (< 11 500 per uL) was found in 89% of patients with NA. Of these patients, 17 (77%) had a WBC count of < 9000 per uL, and 8 (36%) had a WBC count < 8000 uL. Of those patients with pathology-confirmed appendicitis, only 8.2% (68 of 825) had a WBC count < 9000 per uL, and 5.2% (43 of 825) had a WBC count < 8000 per uL. The authors used this data to construct receiver operating characteristic (ROC) curves* for the use of WBC count as predictor of appendicitis. A threshold WBC of 9000 per uL correlated with a sensitivity for appendicitis of 92% (95% CI: 90-93%), and reduced the negative appendectomy rate by 77%, while a WBC threshold of 8000 per uL the sensitivity was increased to 95% (95% CI: 92-97%), reducing the negative appendectomy rate by 36%.

By Emilia Hermann and Leah H. Carr

* ROC curves plot the fraction of true positives versus false positives at different threshold values. The area under an ROC curve demonstrates the probability that a true positive event will be detected over a negative event, essentially acting as a measure of test accuracy such that an area closer to 1 is closer to perfectly accurate.

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