Short Attention Span Summary
Surgeon: "It's not appendicitis. The white count is normal."
You: "I hate you..."
The overall diagnostic performance (area under the curve, AUC) of total white blood cell (WBC) count and absolute neutrophil (ANC) count varied with age. Younger kids had poorer overall performance: < 5 years AUC = 0.69; 5-11 years AUC = 0.76; 12-18 years AUC = 0.83. Younger kids tended to have higher sensitivity but lower specificity at any given WBC cutoff. Older kids tended to have lower sensitivity and higher specificity at any WBC cutoff. Why does this matter? Pediatric appendicitis scoring systems should probably use age-adjusted WBC cutoffs. Also importantly, kids can have appendicitis and a normal WBC count.
Let's look at an example with the numbers from this study. A 7 year old presents with suspicion of appendicitis and has a WBC of 9,000, which is below our preset cutoff of 10,000. Prevalence of disease in this study was 41%; at a WBC of 9,000, the negative likelihood ratio is 0.12. That means his post-test probability of appendicitis is 7.8%. If we do the same scenario with a 15 year old, the post-test probability of appendicitis is 7.4%. If we do the same for a 4 year old, the post-test probability of appendicitis is 6.9%. What does this mean? The normal WBC count is helpful, but we are still left with a roughly 7-8% probability of appendicitis, which is too high to consider it "ruled out."
Pediatric appendicitis scoring systems should use age-adjusted WBC cutoffs. Another take home is to recognize the limitations of WBC count in ruling out appendicitis. A normal WBC count decreases the post-test probability of disease but doesn't rule it out. Evidence Care has an excellent pediatric appendicitis module with all the major appendicitis scores and helps you decide what imaging strategy to employ, if any. It's pretty slick!
Acad Emerg Med. 2016 Nov;23(11):1235-1242. doi: 10.1111/acem.13018. Epub 2016 Oct 31.
1Division of Emergency Medicine, Children's Hospital Boston and Harvard Medical School, Boston, MA.
2Department of Pediatrics, Columbia University College of Physicians and Surgeons, New York, NY.
3Department of Pediatrics, University of Utah School of Medicine, Salt Lake City, UT.
4Department of Pediatrics, University of Colorado School of Medicine, Denver, CO.
5Department of Pediatrics, University of Louisville, Louisville, KY.
6Department of Pediatrics, Baylor College of Medicine, Houston, TX.
7Department of Pediatrics, Children's Hospital of Philadelphia and Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA.
8Department of Pediatrics, Alfred I. DuPont Hospital for Children, Wilmington, DE.
9Division of Emergency Medicine, Children's Mercy Hospitals and Clinics, Kansas City, MO.
10Department of Pediatric Emergency Medicine, Children's Hospital and Clinics of Minnesota, Minneapolis, MN.
White blood cell (WBC) count and absolute neutrophil count (ANC) are a standard part of the evaluation of suspected appendicitis. Specific threshold values are utilized in clinical pathways, but the discriminatory value of WBC count and ANC may vary by age. The objective of this study was to investigate whether the diagnostic value of WBC count and ANC varies across age groups and whether diagnostic thresholds should be age-adjusted.
This is a multicenter prospective observational study of patients aged 3-18 years who were evaluated for appendicitis. Receiver operator characteristic curves were developed to assess overall discriminative power of WBC count and ANC across three age groups: <5, 5-11, and 12-18 years of age. Diagnostic performance of WBC count and ANC was then assessed at specific cut-points.
A total of 2,133 patients with a median age of 10.9 years (interquartile range = 8.0-13.9 years) were studied. Forty-one percent had appendicitis. The area under the curve (AUC) for WBC count was 0.69 (95% confidence interval [CI] = 0.61 to 0.77) for patients < 5 years of age, 0.76 (95% CI = 0.73 to 0.79) for 5-11 years of age, and 0.83 (95% CI = 0.81 to 0.86) for 12-18 years of age. The AUCs for ANC across age groups mirrored WBC performance. At a commonly utilized WBC cut-point of 10,000/mm3 , the sensitivity decreased with increasing age: 95% (<5 years), 91% (5-11 years), and 89% (12-18 years) whereas specificity increased by age: 36% (<5 years), 49% (5-12 years), and 64% (12-18 years).
WBC count and ANC had better diagnostic performance with increasing age. Age-adjusted values of WBC count or ANC should be considered in diagnostic strategies for suspected pediatric appendicitis.
© 2016 by the Society for Academic Emergency Medicine.
PMID: 27251399 [PubMed - in process]