Diagnostic value of C-reactive protein in suspected acute appendicitis--a prospective case control study

To find out the Sensitivity, Specificity and Predictive value of C-reactive protein in the diagnosis of acute appendicitis.

Hundred patients undergoing emergency appendicectomy were cases and thirty patients undergoing interval appendicectomy during the same period were controls. Creactive protein was measured pre-operatively.

CRP was reactive in 89% of cases and 3 of 30 controls (P = 0). Among the thirteen complicated cases, two had a CRP reactivity of 1.2 mg/dl, eight had 2.4 mg/dl and three had 3.6 mg/dl. In the uncomplicated cases, forty nine were reactive at 1.2 mg/dl, twenty six at 2.4 mg/dl and one at 3.6 mg/dl (P = 0.0009). In histopathologically inflamed appendix, reactivity was 94.4% and in normal appendix reactivity was 40% (P = 0.00007). CRP positivity had a sensitivity of 94.4% (CI 89.9-98.9) and a positive predictive value of 95.5% (CI 91.4-99.6). CRP reactivity and leucocytosis if combined, the sensitivity, specificity, PPV and NPV were 85%, 100%, 100% and 81% respectively. Threshold for CRP reactivity if raised to 2.4 mg/dl, the sensitivity, specificity, PPV and NPV are 42%, 100%, 100% and 16% respectively.

CRP estimation is a good 'rule-in' test and not-so-good 'rule-out' test to diagnose acute appendicitis.