Accuracy of White Blood Cell Count and C-reactive Protein Levels Related to Duration of Symptoms in Patients Suspected of Acute Appendicitis.

OBJECTIVES Low levels of white blood cell (WBC) count and C-reactive protein (CRP) have been suggested to sufficiently rule out acute appendicitis. The diagnostic value of these tests is likely to depend on the duration of complaints. The aim of this study was to evaluate the accuracy of these inflammatory markers in relation to duration of symptoms in patients suspected of acute appendicitis. METHODS Patients suspected of having acute appendicitis were retrospectively selected from five prospective cohorts of patients with acute abdominal pain presenting at the emergency department (ED) in two European countries. Only adult patients with clinical suspicion of acute appendicitis based on medical history, physical examination, and laboratory studies at the time of registration in the original cohorts were included in this analysis. WBC count and CRP level were determined in all patients and a final diagnosis was assigned to every patient by an expert panel based on all available clinical data and follow-up. For categories based on symptom duration, the diagnostic accuracy of single and combined cutoff values was determined, and negative predictive values (NPV) and positive predictive values (PPV) were calculated. Subgroup analyses for age (<40 years or ≥40 years) and sex were performed. RESULTS A total of 1,024 patients with clinically suspected acute appendicitis were included, of whom 580 (57%) were assigned a final diagnosis of appendicitis. No value of WBC count, CRP level, or their combination resulted in a NPV of more than 90%, regardless of the duration of symptoms. A WBC count of >20 × 10(9) /L in combination with symptoms for more than 48 hours was associated with a PPV of 100%. However, only eight of the 1,024 patients (1%) fulfilled these criteria, limiting the clinical applicability. No other cutoff level of WBC count, CRP level, or their combination resulted in a PPV of more than 80%, regardless of the duration of symptoms. In female patients, normal levels of CRP and WBC count more accurately excluded the diagnosis of appendicitis than normal levels did in male patients. CONCLUSIONS No WBC count or CRP level can safely and sufficiently confirm or exclude the suspected diagnosis of acute appendicitis in patients who present with abdominal pain of 5 days or less in duration.