Reliability of C-reactive protein measurement in general practice in The Netherlands

High-sensitivity serum C-reactive protein levels in subjects with or without myocardial infarction or periodontitis

BACKGROUND

Serum high-sensitivity C-reactive protein (hsC-rp) is a non-specific marker of inflammation. Elevated hsC-rp levels are found in subjects with cardiovascular diseases (CVDs). Periodontitis may influence hsC-rp levels.

OBJECTIVES

To assess periodontal status and hsC-rp serum levels in consecutive subjects hospitalized and diagnosed with acute myocardial infarction (AMI) (n=85) and in a group of carefully matched subjects (gender, age social, ethnic, and smoking habits) without clinical evidence of CVD (n=63).

METHODS

hsC-rp levels, other routine serum values, and clinical periodontal conditions were studied.

RESULTS

Subjects with AMI had higher hsC-rp levels than control subjects (p<0.001, Mann-Whitney U-test). The odds that subjects in the control group with periodontitis (30% or more sites with>4.0 mm loss of alveolar bone) had serum hsC-rp>1.8 mg/l was 1.5 (95% CI: 1.1-7.3, p<0.05). Stepwise linear regression analysis failed to include periodontal parameters in an explanatory model to hsC-rp values. Only the serum leucocyte (white blood cell (WBC)) counts were explanatory to hsC-rp values (beta standard coefficient=0.45, t=3.2, p<0.001). Serum WBC counts were significantly higher in control subjects with periodontitis (p<0.03) but not in subjects in the AMI group (p<0.57).

CONCLUSIONS

(1) As expected, elevated serum hsC-rp concentration and serum WBC counts are associated with acute coronary heart disease. (2) Elevated serum hsC-rp values are associated with radiographically defined periodontitis in subjects with no evidence of CVD. (3) Periodontal parameters are not explanatory to elevated serum hsC-rp values if serum WBC and low-density lipoprotein counts are included in the regression model.

[Reproducibility of C-reactive protein analyses]

The aim of this study was to measure the reliability of different nephelometric techniques for measuring C-reactive protein (CRP). One hundred and twenty samples were obtained from 40 patients. All 120 samples were divided in three parts to measure CRP using three different methods. Reliability was determined by the kappa index and intraclass correlation coefficient. The intraclass correlation coefficient ranged from 0.78 to 0.94. When CRP values were categorized in four groups, the kappa index reached 75-86% and percentage of agreement varied from 95% to 97%. When CRP values were divided into two groups, the kappa index was 73% to 78% and the percentage of agreement was 86% to 89%. We found that CRP determinations with different nephelometric methods were highly reproducible, even when different analysts were involved. Ultrasensitive techniques are needed only if the clinical objective is to obtain a CRP measurement under 0.3 mg/dl.

Evaluation of a near-patient test for C-reactive protein used in daily routine in primary healthcare by use of difference plots

We have assessed the technical performance and robustness of NycoCard® CRP Whole Blood, a near-patient test for C-reactive protein (CRP), when used in realistic daily routine situations in general practice clinics (GPC). Thirteen GPCs participated, five of them with technician staff. From 898 patients, split-sample measurements for CRP were made. Results from GPCs were compared with results from a turbidimetric laboratory method, traceable to international reference preparations (IFCC CRM 470). Results were evaluated in difference plots where the expected distribution, due to an estimated analytical variation, was compared with measured differences. Of all difference points, 91.5% (n = 819) were within a 95% prediction interval based on the imprecision of both methods. Mean bias (95% confidence interval) was −0.3 mg/L (−0.9 to 0.3). No differences in analytic quality were found between GPCs with technician staffs and GPCs without, and between test results obtained within the first and second week, compared with the rest of the study period. We find the test as good when used in GPCs as could be expected from laboratory testing, and consequently robust, which is a necessity for use in routine situations in general practice. General application of difference plots in test evaluations are discussed in detail.

The fat emulsion agglutination test: a reliable and cost effective alternative to the latex agglutination test for rapid bedside CRP measurement

We compared two tests for bedside C reactive protein (CRP) measurement: the latex agglutination test (LAT) and the fat agglutination test (FAT). FAT is based on the property of CRP to agglutinate fat emulsions in the presence of CaCl2. The sensitivity, specificity and accuracy of FAT and LAT to detect a CRP > 10 mg/l, determined with radial immunodiffusion (n = 500 pediatric patients, CRP range 0- > 80 mg/l), were 91%, 82% and 90% respectively for FAT and 82%, 95% and 85% for LAT. FAT reagent could be stabilized with NaN3 (0.02%) for at least one year, when stored at 4 degrees C (n = 49). NaN3 (0.02%) had no effect on agglutination of FAT (n = 40). In conclusion, in pediatric patients, FAT is a reliable and cost effective alternative to LAT, if serum samples are used.

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-1: 8.2%, B-2: 12.4%, B-3,4: 6.5%, C-1: 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.

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 general practitioner (GP) with a new complaint for which the GP considers determination of the erythrocyte sedimentation rate (ESR) to be indicated. During 4 successive months in 1992, 11 GPs in four general practice centres in the Netherlands identified patients indicated for the erythrocyte sedimentation rate. ESR and CRP were determined at the local hospital laboratory. One year later, an independent GP established the follow-up diagnoses. By comparing the test results with the follow-up diagnoses, using logistic regression analysis and Receiver Operating Characteristic curves, sensitivities, specificities, predictive values and odds ratios were established. In 396 patients the prevalence of inflammatory diseases and malignancies ('pathology') was found to be 26% in males and 15% in females. Both ESR and CRP were valuable in discriminating pathology from harmless, often self-limiting diseases. The optimal upper limits of reference values ('cut-off points') for ESR were found to be 31 mm in both males and females. At these cut-off points, the diagnostic gains from positive and negative test results (positive predictive value minus prevalence, and negative predictive value minus 100% minus prevalence) were 45% and 4% for males and 30% and 2% for 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 positive and negative test results were 18% and 9% in males and 25% and 4% in females.(ABSTRACT TRUNCATED AT 250 WORDS)