Avoiding negative appendectomies in rural surgical practice: is C-reactive protein estimation useful as a diagnostic tool?

Background: Appendectomy is one of the most frequently performed abdominal operations in rural surgical practice. In spite of various preoperative investigations to aid in the diagnosis, the rate of negative appendectomies is 15%-30%. Qualitative C-reactive protein (CRP) estimation is an inexpensive diagnostic test which can be done in small laboratories using a simple kit. We studied the value of estimating the CRP level in diagnosing acute appendicitis and reducing negative appendectomies.

Methods: Patients who had been clinically diagnosed with acute appendicitis and planned for appendectomy, were selected by purposive sampling. Leucocyte counts, CRP level estimation and ultrasonography of the abdomen were done preoperatively. The sensitivity, specificity, predictive value, diagnostic accuracy, false-positive and false-negative rates, and likelihood ratios were calculated for various components of the diagnosis.

Results: Of the 238 patients, 193 had histological evidence of acute appendicitis. When the diagnosis was based on the consultant's decision, the overall negative appendectomy rate was 18.9%. CRP level estimation yielded a sensitivity of 98% (95% CI 95%-100%) and specificity of 87% (95% CI 73%-94%). A positive CRP value was associated with acute appendicitis (p<0.0001). Adding CRP to the diagnostic work-up increased the sensitivity to 100% (95% CI 98%-100%) and diagnostic accuracy to 92% (95% CI 87%- 95%), and would have reduced negative explorations to 3%.

Conclusion: CRP estimation complements the clinical diagnosis by a consultant surgeon, and should be included in the diagnostic work-up of appendicitis. CRP estimation is inexpensive and does not add an undue burden to the cost of management.