C-reactive protein in general practice - How commonly is it used and why?

Objective - C-reactive protein (CRP) is a well-known diagnostic tool in general practice. The scope of this study was to assess how frequently CRP is used by general practitioners and to evaluate the reasons for using it. Design - A retrospective part based on data from a laboratory database system, and a prospective part with a questionnaire-based registration. Setting - 30 general practice clinics in the catchment area of Vejle County Central Hospital. Subjects - Retrospectively, all patients from general practice serviced by the laboratory for one year. Prospectively, 1190 patients from whom a blood sample was taken for CRP-measurement during a 2 month study period. Main outcome measures - The frequency of using CRP and the reason requesting it; A) diagnosing a new disease, B) monitoring a well known disease, or C) ''screening''. Furthermore; 1) infections, 2) chronic inflammatory disease, 3) malignant disease, or 4) others. Results - CRP-measurements were ordered in 3.7% of all consultations in general practice and for 34.1% of all patients whose blood sample was analysed at the central laboratory. The use of CRP was as follows: A-1: 28.6%, A-2: 6.7%, A-3,4: 9.3%, B-l: 8.2%, B-2: 12.4%, B-3,4: 6.5%, C-l: 5.7%, C-2: 3.2%, C-3: 3.5% and C-4: 15.2%. Diagnosing a new (infectious) disease was the most frequent single reason for CRP-measurement. There was major interpractice variation. Conclusions - CRP is frequently used in general practice, mostly (65.4%) in the field of infections and chronic inflammatory diseases. Because of major interpractice variation, the most correct way of using CRP should be evaluated and guidelines should be provided.