Biologic variability of C-reactive protein: is the available information reliable?

BACKGROUND: C-reactive protein (CRP) is recognized as a marker of cardiovascular risk. The biologic variability of CRP is crucial to understanding its significance in estimation of individual risk and subsequent changes in serial analyses.
METHODS: We systematically reviewed publications on biologic variation of CRP to evaluate the consistency of available data. Data was evaluated with attention to number and type of enrolled subjects, duration of study, frequency of sample collection, sample type, sample storage, analytical methodology, assay sensitivity and statistical analysis.
RESULTS: A total of eleven studies on CRP biologic variability were recruited from literature. The majority of studies were limited by choice of analytic methodology, population selection, protocol application, and statistical analysis. Unfortunately, the only study that fulfilled all major pre-analytical, analytical and post-analytical requirements derived biologic variability from logarithmically transformed data, thus making application to clinical practice difficult.
CONCLUSIONS: There is a paucity of robust data on biologic CRP variability in serum. It is obvious that additional well defined studies are needed to define reliable values of reference change values and of number of samples required to estimate the individual's cardiovascular risk by CRP.