The mean age of participants was 38 years (SD, 16.5). Fifty percent of the study population was female and 48% were of non-Hispanic white race/ethnicity. The mean time between examinations was 18.9 days. Mean CRP was 0.45 mg/dL (95% CI: 0.39–0.51) at the first examination and 0.43 mg/dL (95% CI: 0.38–0.49) at the second examination (p-for-difference=0.45). The Spearman’s correlation between visits was 0.65, the ICC was 0.77 (95% CI: 0.69–0.84), and the CVw
was 46.2% (95% CI: 42.9–49.3%). The high variability in CRP can be seen visually on the scatterplot (), although the Bland-Altman plot shows that most of the discordance between examinations occurred at higher values (>1.0 mg/dL) (eFigure 1
). The variability was particularly high among persons with CRP >2.0 mg/dL.
Scatterplot of CRP measurements in a subsample of NHANES 2001–2002
The prevalence of elevated CRP ≥1 mg/dL was 10.5% at the first examination and 10.4% at the second; 7.2% of participants had persistently elevated CRP (eTable 1
). Of those with normal CRP at the first examination, only 3.5% had CRP ≥1 mg/dL at the second. Of those with CRP ≥1 mg/dL at the first examination, 32% were reclassified as having CRP <1 mg/dL at the second. The prevalence of CRP ≥2 mg/dL at the first examination was 4.3% and was 2.8% at the second; 1.5% of participants had CRP ≥2 mg/dL at both examinations, representing an approximately 65% decrease in prevalence.