The assessment of laboratory tests in the diagnosis of acute appendicitis.

A comparison of laboratory tests was undertaken in 106 patients admitted to the emergency room with the tentative diagnosis of acute appendicitis and who subsequently underwent appendectomy. The tests examined included the total white blood cell count, manual differential count, cytochemical differential count, and C-reactive protein. The sensitivity, specificity, efficiency, and predictive value of these tests in the diagnosis of acute appendicitis were calculated. The cytochemically determined neutrophil count, when greater than the upper limit of the reference interval of either 75% or 7.88 X 10(9)/L, and the total white blood count greater than the upper limit of the reference interval of 10.5 X 10(9)/L were the single best tests for the diagnosis of acute appendicitis with the highest sensitivities of all tests examined (81-84%). The manual differential count and C-reactive protein showed significantly lower sensitivities. Test combinations also were examined. The combinations consisted of two or more tests joined by an "or" rule, i.e., if any one of the individually linked tests of the combination is above the reference interval, the combination is considered as indicating acute appendicitis. When either of the following test combinations were utilized--(1) total white count greater than 10.5 X 10(9)/L or cytochemical neutrophils greater than either 75% or 7.88 X 10(9)/L or CRP greater than 1.2 mg/dL; (2) total white count greater than 10.5 X 10(9)/L or manual bands greater than either 11% or 1.15 X 10(9)/L or CRP greater than 1.2 mg/dL--the sensitivity of the combination in the diagnosis of acute appendicitis approached 100% with a specificity in the range of 50%. We suggest that these test combinations may be useful in deciding which patients need further observation and reexamination prior to surgery. We also suggest the need for further studies to assess the usefulness of these tests in other types of acute inflammation and infection.