Rapid determination of C-reactive protein levels: semiquantitative versus quantitative

The use of CRP tests in patients with respiratory tract infections in primary care in Sweden can be questioned

A diagnosis-antibiotic prescribing study was performed in 5 counties in Sweden during 1 week in November in 2000 and 2002 respectively. As a part of the study, the use and results of C-reactive protein (CRP) tests in relation to duration of symptoms and antibiotic prescribing in 6778 patients assigned a diagnosis of respiratory tract infections were analysed. In almost half (42%) of the patients, a CRP test was performed. The majority of CRP tests (69%) were performed in patients assigned diagnosis upper respiratory tract infection, where the test is not recommended. Overall, there was a minor decrease in antibiotic prescribing when CRP was used (41%), in comparison to 44% of the patients where no CRP was performed (p < 0.01). Patients assigned diagnoses implying a bacterial aetiology were prescribed antibiotics irrespective of result of CRP or length of symptoms before consultation. For patients assigned viral diagnoses, antibiotic prescribing increased with increasing duration of symptoms and increasing value of CRP. The use of CRP decreased antibiotic prescribing in patients assigned to viral diagnoses and with longstanding symptoms (p < 0.001). However, 59% of the patients assigned viral diagnoses with CRP > or = 25 received antibiotics, which seems to indicate a misinterpretation of CRP and a non-optimal use of antibiotics.

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.

Serum C-reactive protein. A useful and economical marker of immune activation in renal transplantation

This study investigated whether serial daily measurements of serum C-reactive protein (sCRP) in 187 renal allograft recipients could help discriminate episodes of renal dysfunction due to rejection or cyclosporine (CsA) nephrotoxicity and help adjust immunosuppression in the early posttransplant period. Excellent primary graft function was associated with an initial peak of sCRP on day 2 after transplant (median, 29 microg/ml; range, 4 to >200 microg/ml) with a return to <20 microg/ml in all patients by day 5 (median, 7 microg/ml; range, 2-19 microg/ml). Stable graft function (mean creatinine, 155 microg/ml) was accompanied by a median sCRP of 4 microg/ml (range, 1-19 microg/ml). In 30 episodes of rejection responsive to methylprednisolone, sCRP was initially significantly raised to a median of 49 microg/ml (P<0.001) but fell rapidly in response to treatment to a median of 11 microg/ml and continued to fall. In 19 episodes of rejection unresponsive to methylprednisolone, median initial sCRP levels were significantly higher (P<0.001) at 119 microg/ml and were still at a median of 77 microg/ml at the end of the treatment. Twenty-four patients in whom renal dysfunction was associated with CsA nephrotoxicity showed no increase in sCRP concentrations; median sCRP concentrations remained at <5 microg/ml throughout the episodes. A similar pattern was seen in patients with acute tubular necrosis. Serial sCRP measurements provide economical and reproducible evidence of immune activation, help discriminate renal dysfunction due to CsA nephrotoxicity or rejection, and allow appropriate modification of immunosuppressive therapy.

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

The aim of this study was to compare the reliability of the whole blood NycoCard C-reactive protein measurement (CRP) with the erythrocyte sedimentation rate (ESR) in four general practice centres (GPCs) in The Netherlands with 443 patients indicated for ESR. During 4 successive months in 1992 NycoCard CRP was measured in capillary (whole) blood at the GPC. A venous blood sample was then transported to the local hospital laboratory in order to determine CRP turbidimetrically in plasma. Westergren's ESR was measured at the GPC and at the laboratory. The dichotomized CRP values measured at the GPCs corresponded with the laboratory values in 88% of the cases. Kappa was 65% (p < 0.00001). Using a 20 mm cut-off point, ESR values measured at the GPCs and the laboratory corresponded in 96% of cases (Kappa = 90%, p < 0.00001). Interpractice variabilities and learning effects did not influence the results. 'False normal' rates for CRP and ESR were 8% and 1%; 'false elevated' rates were 28% and 12% respectively. The reliability of the NycoCard CRP measurement in whole blood disappointed. In particular the 'false elevated' rate is unacceptably high for daily general practice. The background of the poor reliability remains unclear.

Value of serum C-reactive protein concentrations in febrile children without apparent focus

We examined the value of serum C-reactive protein (CRP) in febrile children without an apparent focus of infection, (i) as a tool to differentiate bacteraemia and bacterial infection from a non-bacterial illness (NBI), and (ii) as an indicator of recovery or complications. Included in the study were 100 children up to the age of 3 years with a temperature of > or = 38.5 degrees C, without an apparent focus. The serum CRP concentration was measured on days 1, 3 and 5 of evaluation and correlated with the final diagnosis and outcome. The serum CRP was 40 mg/l and above in 95% of patients (18/19) with bacteraemia and also in seven of the eight with purulent meningitis, while it was < 40 mg/l in 84% of patients (52/62) with NBI (mean (SD) 22 (28.6) mg/l). The mean serum CRP concentration among six children with a culture-positive urinary tract infection (16.3 (8.3) mg/l) and five with otitis media (9 (5.7) mg/l) was similar to those with NBI. The sensitivity of serum CRP > or = 40 mg/l for diagnosis of bacteraemia was 95% and the positive predictive value 67%. On serial monitoring, a fall in the CRP concentration was a sensitive indicator of recovery from infection and provided the earliest clue to therapeutic response long before a fall in temperature.

C-reactive protein: a new rapid assay for managing infectious disease in primary health care

Quantitative C-reactive protein (CRP) measurement has become increasingly valuable as a test for rapid diagnosis of infections in hospital medicine. CRP has not obtained the same importance in primary health care. This has, at least partly, been due to methodological difficulties, with no simple or rapid tests with quantitative results available. A new immunometric semi-quantitative assay, NycoCard CRP, has recently been developed. CRP was analysed at the local health centres by the new assay in 288 consultations where patients came because of infections. Parallel CRP values were obtained by an established reference method. The two procedures had an acceptable correlation (r = 0.85). The primary care doctors also registered the clinical information they obtained from each CRP result. CRP was helpful in indicating the presence, or absence of bacterial infection in more than half the consultations due to new infections. CRP was thought to yield more clinical information than the erythrocyte sedimentation rate in almost every case.