C-reactive protein as a predictor of severity of appendicitis
Background: Complex (perforated or gangrenous) appendicitis has a high rate of morbidity in South Africa.
Objectives: To determine if CRP is superior to WCC in diagnosing complex appendicitis. Determining an optimal cut-off value for CRP in detecting complex appendicitis.
Methods: The study retrospectively reviewed results from January 2013 to December 2015 at Paarl Hospital in the Western Cape province. All patients who had their appendices surgically removed due to suspected appendicitis and who had preoperative results for CRP and WCC were included. Using the area under the Receiver Operated Characteristics curve we compared the inflammatory markers of 2 groups with histologically proven appendicitis: those with complex (perforated or gangrenous appendix) and those with uncomplicated appendicitis (inflamed appendix). Youden’s J statistic was used to determine the optimal cut-off value above which complex appendicitis would be the most likely diagnosis.
Results: A total of 591 patients were identified, 385 had results for both WCC and CRP. CRP (AUC 72%) proved to be a fair and WCC (AUC 58%) a poor predictor of complex appendicitis. Cut-off values for CRP and WCC were found to be 215 mg/l and 16.80 109 cells/l respectively. At these threshold values CRP (sensitivity 51.4%, specificity 85.7%, p-value < 0.001, positive predictive value 80.2%, negative predictive value 61%, positive likelihood ratio 3.6 and diagnostic odds ratio 6.35) proved to be much better than WCC (sensitivity 43%, specificity 73.8%, p-value = 0.022, positive predictive value 64.9%, negative predictive value 53.4%, positive likelihood ratio 1.64 and diagnostic odds ratio 2.11) in predicting complex appendicitis.
Conclusion: CRP is superior to WCC in the differentiation between uncomplicated and complex appendicitis. Using a cut-off value of CRP 215 mg/l is statistically significant in diagnosing complex appendicitis. This value should be used cautiously as many more studies are needed to confirm these findings.