DIAGNOSTIC-VALUE OF C-REACTIVE PROTEIN MEASUREMENT DOES NOT JUSTIFY REPLACEMENT OF THE ERYTHROCYTE SEDIMENTATION-RATE IN DAILY GENERAL-PRACTICE

The purpose of this paper was to establish the diagnostic value of the C-reactive protein measurement (CRP) in patients attending their gene ral practitioner (GP) with a new complaint for which the GP considers determination of the erythrocyte sedimentation rate (ESR) to be indica ted. During 4 successive months in 1992, 11 GPs in four general practi ce centres in the Netherlands identified patients indicated for the er ythrocyte sedimentation rate. ESR and CRP were determined at the local hospital laboratory. One year later, an independent GP established th e follow-up diagnoses. By comparing the test results with the follow-u p diagnoses, using logistic regression analysis and Receiver Operating Characteristic curves, sensitivities, specificities, predictive value s and odds ratios were established. In 396 patients the prevalence of inflammatory diseases and malignancies ('pathology') was found to be 2 6% in males and 15% in females. Both ESR and CRP were valuable in disc riminating pathology from harmless, often self-limiting diseases. The optimal upper limits of reference values ('cut-off points') for ESR we re found to be 31 mm in both males and females. At these cut-off point s, the diagnostic gains from positive and negative test results (posit ive predictive value minus prevalence, and negative predictive value m inus 100% minus prevalence) were 45% and 4% for males and 30% and 2% f or females. The optimal cut-off point for CRP was found at 15 mg L(-1) in males and 34 mg L(-1) in females. The diagnostic gain from positiv e and negative test results were 18% and 9% in males and 25% and 4% in females. In daily general practice there is no reason to abandon ESR in favour of CRP. Only if a GP wants to be informed of the test result as quickly as possible, and the costs of ordering tests are less impo rtant, might CRP be reconsidered as a test.