The best questions often stem from the inquisitive learner. As educators, we love, and are always humbled by, those moments when we get to say, “I don’t know.” For some of these questions, you may already know the answers. For others, you may never have thought to ask the question. For all, questions, comments, concerns, and critiques are encouraged. Welcome to the Kids Korner.
Question 2: For pediatric patients with suspected appendicitis, can a normal C-reactive protein (CRP) rule out acute appendicitis?
A prospective study by Sengupta et al evaluated the diagnostic accuracy of white blood cell (WBC) count and CRP for acute appendicitis.1 This study included 98 patients, of whom only 20 were pediatric patients. The authors found that a combined normal WBC (lower than 11,000) and a normal CRP (less than 10 mg/L) demonstrated a 100 percent negative predictive value (NPV) in patients younger than 18 years of age. Separately, the sensitivities of an elevated WBC and elevated CRP were 85 percent and 65 percent, respectively, for diagnosing histologically proven acute appendicitis. The authors stated, “No patient with a normal white cell count and CRP needed appendectomy, and therefore, depending on other clinical criteria, these patients do not require admission to the hospital.”
That was a single study with a very small pediatric patient population (n=20 children), and a number of other articles would suggest a different conclusion. For instance, in a single retrospective cohort study from two separate institutions by Vaughan-Shaw et al that included 297 patients (both adults and children), 17 patients with histologically proven acute appendicitis would have been sent home if the exact same criteria for WBC and CRP as stated above were used.2 That’s 5 percent and 8 percent of the histologically proven appendicitis cases from the two institutions examined in that study.
That research included both adults and children. So what have pediatric-specific studies found? A recent prospective study by Zouari et al evaluated 292 pediatric patients with the combination of Alvarado score (see Table 1), CRP, and ultrasound.3 Alone, the sensitivity of CRP was 77 percent, so it is an ineffective test for diagnosing appendicitis. When combining a negative ultrasound (defined as a normal appendix or no appendix visualized) with an Alvarado score of less than 4 and a normal CRP, the NPV was only 92 percent, which is still not a great NPV. The NPV was even worse (73 percent) if the Alvarado score was 5–6. In the end, the negative CRP demonstrated poor diagnostic ability for acute appendicitis.