Comparison of tests for the measurement of C-reactive protein in the low range

C-reactive protein (CRP) has recently been identified as an independent risk factor for cardiovascular disease. The published studies all used highly sensitive immunological assays that were specially designed in-house to measure CRP in the sub-clinical (normal) range. However, these tests are not commercially available. The aim of the present study was to compare the relationship between these laboratory tests and two generally available immunoassays, sold by Kordia (The Netherlands) and Behring (Germany), respectively. A panel of serum samples (n=19) obtained from healthy volunteers was coded, alliquoted and distributed amongst the various sites (Dr. M.P.M. de Maat, Leiden, The Netherlands; Dr. R. Tracy, Vermont MA, USA; and Dr. W. Koenig, Ulm, Germany) for determination. Measurements with the commercial tests were carried out at the TNO Clinical Assays Unit in Leiden, The Netherlands. The reported results of the CRP-measurements were decoded and CRP values (expressed in mg/L) were plotted (see figure). For clarity reasons, the Leiden lab. test was the designated reference test. All test are in high agreement with each other, probably since each uses a reference material calibrated against the WHO First Interational Standard for CRP (85/506). The present findings indicate that both commercial tests are well suited to study the role of CRP as risk factor in cardiovascular and related disorders.