Value Of C-reactive Protein Measurement Research Articles

The added value of C-reactive protein measurement in diagnosing pneumonia in primary care: a meta-analysis of individual patient data.

C-reactive protein (CRP) is increasingly being included in the diagnostic work-up for community-acquired pneumonia in primary care. Its added diagnostic value beyond signs and symptoms, however, remains unclear. We conducted a meta-analysis of individual patient data to quantify the added value of CRP measurement. We included studies of the diagnostic accuracy of CRP in adult outpatients with suspected lower respiratory tract infection. We contacted authors of eligible studies for inclusion of data and for additional data as needed. The value of adding CRP measurement to a basic signs-and-symptoms prediction model was assessed. Outcome measures were improvement in discrimination between patients with and without pneumonia in primary care and improvement in risk classification, both within the individual studies and across studies. Authors of 8 eligible studies (n = 5308) provided their data sets. In all of the data sets, discrimination between patients with and without pneumonia improved after CRP measurement was added to the prediction model (extended model), with a mean improvement in the area under the curve of 0.075 (range 0.02-0.18). In a hypothetical cohort of 1000 patients, the proportion of patients without pneumonia correctly classified at low risk increased from 28% to 36% in the extended model, and the proportion with pneumonia correctly classified at high risk increased from 63% to 70%. The number of patients with pneumonia classified at low risk did not change (n = 4). Overall, the proportion of patients assigned to the intermediate-risk category decreased from 56% to 51%. Adding CRP measurement to the diagnostic work-up for suspected pneumonia in primary care improved the discrimination and risk classification of patients. However, it still left a substantial group of patients classified at intermediate risk, in which clinical decision-making remains challenging.

Clinical value of C-reactive protein measurements in HIV-positive patients

The acute-phase protein C-reactive protein (CRP) is a sensitive marker of inflammation and tissue damage. We measured CRP in 109 HIV-1 antibody-positive patients admitted to hospital for investigation. In 67 patients with intercurrent infection (of whom 27 were afebrile at presentation) CRP levels were 2.2-483.5 mg/dL (normal value in the general population <3 mg/dL) and in 42 patients with alternative non-infection diagnoses CRP levels were 0.5-108.6 (median=5.9) mg/dL. Whereas in those with infections elevated CRP levels fell in response to specific therapy, values remained abnormal in those with non-infection diagnoses. CRP appears useful for diagnosis and monitoring of intercurrent infection in HIV-1 antibody-positive patients. In HIV-1 antibody-positive patients without intercurrent infection, CRP values higher than in the general population possibly reflect a sustained acute-phase response as a consequence of HIV infection per se.

Value of C-reactive protein measurements in exacerbations of chronic obstructive pulmonary disease

C-reactive protein (CRP) has been shown to be a useful and sensitive indicator of pyogenic infections in many clinical situations, including acute pneumonia and infective pulmonary exacerbations in cystic fibrosis patients. Exacerbations of COPD are often, but not always, associated with demonstrable infection. The value of CRP measurement in this situation has not been assessed. We have evaluated CRP measurement in 50 patients [age 71 ± 8 ( sd) years] who were admitted to hospital with clinical evidence of exacerbation [ PaO 2=7·3 ± 1·3 ( sd) kPa, baseline FEV 1=0·8 ± 0·4 ( sd) 1]. These patients all had serial measurement of CRP [polarizing immunofluorescence (Abbot, TDx)], peripheral white cell count (WCC), body temperature, peak expiratory flow rate, Karnofsky performance status and chest X-ray, in addition to serial sputum bacteriological analysis carried out in a specialized laboratory. CRP was elevated ( > 10 mg 1 −1) in all patients ( n=29) with proven infection [103 ± 98 ( sd) mg 1 −1]. Levels were markedly elevated in patients infected with Streptococcus pneumoniae (mean 156 mg 1 −1); there was also a rapid fall in the CRP with therapy. WCC fell with therapy, giving a correlation with CRP level ( r=0·44, P<0·01). Since CRP elevation was observed in patients having exacerbation with proven infections and also in those where infection was not proven, it is possible that, while it is a marker for COPD exacerbation, it is not necessarily a marker of bacterial infection per se. However, it is evident from our study that it is of value in the assessment of exacerbations of COPD, where routine bacterial culture of sputum is often unreliable, and thus the measurement of serum CRP may provide an additional objective indicator of infection.

The value of C-reactive protein measurement in rheumatoid arthritis

Since 1973, assessment of serum concentrations of C-reactive protein (CRP) has been advocated as a objective measure of disease activity in rheumatoid arthritis (RA). Our review of clinical experience with CRP measurement suggests it has at least two important roles to play in the management of RA. First, persistently elevated CRP levels have prognostic value. In general, such elevated levels are found in those patients who are at greater risk for continuing joint deterioration and therefore may need more aggressive treatment and supportive care. Second, in general, improvement in CRP levels is an objective indication that a drug has produced a beneficial effect and thus may be useful to the physician for monitoring effects of therapy. Since CRP may be elevated in a number of conditions besides RA, a diagnosis of RA must be made before using CRP as a prognostic factor.

Acute phase response: Biologic and clinical significance

It has been known for several centuries that significant alterations in the composition of blood take place in diseases characterized by tissue injury and/or inflammation. These changes, collectively referred to as the acute phase response, have received a great deal of attention in recent years, both with respect to biologic mechanisms involved and diagnostic utility of the respective changes, as studied in clinical laboratories. This issue of the Clinical Immunology Newsletter is devoted to a discussion of both of these aspects of the acute phase response. The article by Dr. Irving Kushner provides a biologic and historical perspective of the acute phase response with an emphasis on the mechanisms, particularly the role of various cytokines, involved in this complex series of reactions. This is followed by three articles that deal with the diagnostic utility of changes in protein composition, as seen during the acute phase response. Dr. Carl Jolliff discusses the application of gel electrophoresis and serum protein electrophoresis in the study of acute and chronic inflammatory states with appropriate illustrations, and the diagnostic utility of changes in haptoglobin levels is discussed by Dr. Frederick Van Lente. Finally; my own article on C-reactive protein (CRP) discusses the value of CRP measurements in various clinical disease entities.