Prospective evaluation of C-reactive protein in patients suspected to have acute appendicitis.

C-reactive protein (CRP) was measured in 70 consecutive patients hospitalized with the diagnosis of acute appendicitis. Of these, 28 patients (Group 1) had acute appendicitis, 25 patients (Group 2) had no identifiable focus of infection and improved with general supportive care, and 17 patients (Group 3) had an identifiable cause for their illness, though not appendicitis. CRP level was not helpful in distinguishing among patients in any group when symptoms were present for 12 hours or less. When symptoms were present for more than 12 hours, all patients in Groups 1 and 3 and half of the patients in Group 2 had a significant increase in CRP value. Thus, a normal CRP value in a patient presenting with a duration of symptoms of more than 12 hours occurred only in Group 2; this difference was statistically significant (P less than 0.001). When symptoms are present for more than 12 hours, an increased CRP value supports the diagnosis of acute appendicitis and will identify patients who have signs and symptoms similar to acute appendicitis but who have another identifiable illness. When the CRP value is normal in a patient who has had symptoms for more than 12 hours, this patient does not have acute, appendicitis and can be followed in an outpatient setting.