title: Intra-individual variability of high-sensitivity C-reactive protein: age-related variations over time in Japanese subjects.
abstract: BACKGROUND
  Prospective studies have demonstrated a direct association between the baseline level of high-sensitivity C-reactive protein (hsCRP) and the risk of developing cardiovascular disease. The potential for hsCRP variability during the follow-up interval is of great interest, so the repeatability of measurements of hsCRP in men and women, and in different age groups, was investigated in the present study.
  
  
  RESULTS
  The measurement of hsCRP was performed in 899 male and 780 female Japanese civil servants aged 18-60 years in the spring of 2004 and 2005. Within-subject repeatability and intra-class correlation coefficient of reliability were used to characterize the variation in measurements. Error of the measurement process was negligible, as the analytical variance was 0.0003 [ln(mg/L)] [ln(mg/L)] with a reliability coefficient of 0.997. In contrast, the within-subject variation of hsCRP was considerable with a reliability coefficient of 0.61 in both sexes and repeatability coefficients of 5.25 and 5.38 in men and women, respectively. The variation differed with age, especially in women, as less variation was observed in subjects over 40 years of age during the follow-up interval.
  
  
  CONCLUSIONS
  The results suggest that a single measurement of hsCRP is subject to considerable but equal within-subject variation over time in men and women, and this variation differs among the age groups, which may affect the risk assessment of hsCRP in association with future cardiovascular events.
authors.affiliation: Department of Welfare Promotion and Epidemiology, Faculty of Medicine, University of Toyama, Toyama, Japan. moaddeli@ms.toyama-mpu.ac.jp
authors.forename: Ali
authors.initials: A
authors.lastname: Nasermoaddeli
authors.forename: Michikazu
authors.initials: M
authors.lastname: Sekine
authors.forename: Sadanobu
authors.initials: S
authors.lastname: Kagamimori
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002097:C-Reactive Protein / Q000032:analysis* / Q000592:standards; D002318:Cardiovascular Diseases / Q000175:diagnosis; D005260:Female; D006801:Humans; D007564:Japan; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012737:Sex Factors; D011795:Surveys and Questionnaires
chemical_list: D002097:C-Reactive Protein