Five-year intra-individual variability in C-reactive protein levels in a Japanese population-based study: the Jichi Medical School Cohort Study at Yamato, 1993-1998.

C-reactive protein (CRP) is an acute-phase reactant that is related to future cardiovascular events. However, little is known about the long-term intra-individual stability of CRP in community residents. The 5-year intra-individual correlation of CRP levels was examined in the Jichi Medical School Cohort Study in Japan. CRP measurements were obtained in 1993 and in 1998 from 388 presumptively healthy individuals aged 30-69 years at baseline. The Pearson's correlation coefficient of CRP between baseline and follow-up measurements was 0.43 (95% confidence interval (CI): 0.34-0.51). Additional analyses by sex and smoking status at baseline revealed similar coefficients. The correlation coefficient of CRP was lower than that of other classical risk factors, such as body-mass index (BMI), blood pressure, and total and high-density lipoprotein (HDL) cholesterol. A subgroup of individuals with higher levels of CRP at both baseline and follow-up measurements had higher BMI, hemoglobin Alc, and plasma fibrinogen, and lower levels of HDL-cholesterol than others, even after adjusting for age, sex, and smoking status in a multiple logistic model. In conclusion, the stability of CRP levels was statistically significant in a long-term population-based study. A subgroup with higher levels of CRP who had an aggregation of cardiovascular risk factors was identified by the 2 measurements.