Incidence of normal white cell count and C-reactive protein in adults with acute appendicitis

Normal C-reactive protein (CRP) and white cell count (WCC) are often used to exclude a diagnosis of acute appendicitis in the Emergency Department (ED). Retrospective review of 281 adult patients with acute appendicitis was performed to study the incidence of normal CRP and WCC on admission and examine any possible predisposing factors.

Retrospective analysis of patient clinical records yielded CRP, WCC, operative diagnosis, time of symptom onset, imaging results and history and examination features. Case-control analysis was performed with patients with normal CRP and WCC considered the case group and those with raised CRP or WCC considered controls. Groups were compared using Mann-Whitney U-test and chi-squared analysis.

Of 281 consecutive patients with histologically proven appendicitis, 24 (8.54%) had normal CRP and WCC on presentation to ED. There were no significant differences in age, sex or time to blood collection between groups. Three patients had normal WCC and CRP and an Alvarado score of 4 or less on presentation. Three patients had persistently normal CRP and WCC on repeated testing. There was a trend towards earlier presentation in patients with normal CRP and WCC with 75.0% versus 58.4% presenting within 24 h of symptom onset (OR 2.14, P = 0.112).

Acute appendicitis remains diagnostically challenging and cannot be excluded on the basis of normal CRP and WCC. Serial clinical and biochemical assessment is warranted in patients with acute abdominal pain, particularly in those presenting early after symptom onset.