High sensitivity C-reactive protein: Biological variations and reference limits

Serum C-reactive protein (CRP) concentration was determined for 3605 subjec ts using an immunonephelometric assay improved to provide greater sensitivi ty. Subjects were from 5 to 75 years old and belonging to 1003 nuclear fami lies recruited from the Stanislas Cohort Study between January 1994 and Aug ust 1995. Sample values for CRP ranged from 0.17 mg/l to 100 mg/l. Geometri c means (mean -SD; mean + SD) were in the 5-14 years old group 0.37 (0.17-1 .07) mg/l, in the 15-28 years old group 0.47 (0.17-1.38) mg/l and in the 29 -75 years old group 0.98 (0.34-2.85) mg/l. For women, the geometric means w ere 0.38 (0.17-1.10) mg/l, 0.62 (0.20-1.90) mg/l and 0.98 mg/l (0.31-3.13) mg/l respectively. The interindividual variability ranged from 138% to 759% among different age classes. Biological factors associated with CRP concen tration variations were examined and accounted for 25% of the CRP variabili ty in men and 40% in women. The main biological factors statistically assoc iated with CRP concentration variations in men were: drugs, leukocyte count , body mass index, tobacco consumption, age, and in women: drugs, leukocyte count, age, body mass index and hemoglobin concentration. These factors we re used to define the exclusion and partition criteria when obtaining the r eference samples. Medians for reference values ranged from 0.20 to 0.68 mg/ l in males and from 0.20 to 0.78 mg/l in women.