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Clinical and Diagnostic Laboratory Immunology, July 2003, p. 652-657, Vol. 10, No. 4
1071-412X/03/$08.00+0     DOI: 10.1128/CDLI.10.4.652-657.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Analytical Performance of a Highly Sensitive C-Reactive Protein-Based Immunoassay and the Effects of Laboratory Variables on Levels of Protein in Blood

Najib Aziz,1,2 John L. Fahey,2 Roger Detels,3 and Anthony W. Butch1*

Clinical Immunology Research Laboratory, Department of Pathology and Laboratory Medicine,1 Center for Interdisciplinary Research in Immunology and Disease, Department of Microbiology and Immunology, David Geffen School of Medicine,2 Department of Epidemiology, School of Public Health, University of California at Los Angeles, Los Angeles, California3

Received 5 February 2003/ Returned for modification 14 March 2003/ Accepted 24 April 2003

C-reactive protein (CRP) is an acute-phase reactant whose levels increase in response to a variety of inflammatory stimuli. Elevated levels in serum are observed after trauma, tissue necrosis, infection, surgery, and myocardial infarction and are associated with an increased risk of cardiovascular disease. CRP levels are also elevated in noninflammatory states, such as obesity, sleep disturbances, depression, chronic fatigue, aging, and physical inactivity. In this study, the performance of a highly sensitive CRP enzyme immunoassay was evaluated, along with common laboratory variables (specimen type, processing time, and storage conditions) that may influence measured blood concentrations of CRP. The measurement range of the assay was from 0.4 to 50 µg/liter. Total imprecision (coefficient of variation) ranged from 8.1 to 11.4%. CRP levels obtained with the enzyme immunoassay were highly correlated with those obtained with an automated immunonephelometric assay. Comparable results were obtained for plasma (heparin and EDTA treated) and serum samples, and levels were unaffected by delays in sample processing and storage temperature. CRP levels were also unaffected by up to seven freeze-thaw cycles. The median CRP concentration in healthy adults was determined to be 0.94 mg/liter, with a 95% working reference interval of 0 to 6.9 mg/liter. In view of these data, we recommend that serial serum or plasma samples for CRP should be stored at 4oC for short periods of time or at -70oC for longer periods and tested within the same run to minimize interassay variability.

* Corresponding author. Mailing address: Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, University of California at Los Angeles, 10833 Le Conte Ave., Mailroom A7-149 CHS, Los Angeles, CA 90095-1713. Phone: (310) 206-0587. Fax: (310) 794-4864. E-mail: abutch{at}mednet.ucla.edu.

Clinical and Diagnostic Laboratory Immunology, July 2003, p. 652-657, Vol. 10, No. 4
1071-412X/03/$08.00+0     DOI: 10.1128/CDLI.10.4.652-657.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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