The clinical characteristics of groups 1 through 5 are shown in the Table, including the characteristics of the patients in groups 3 and 4 at the second CRP measurement 2 and 6 years, respectively, after the first measurement. The CRP values of patients in groups 1 through 5 at all sampling times and IL-6 values of the patients in group 1 are plotted in Figure 1. Within-patient variance of CRP values for the 159 patients was considerable (1.79 mg/L [95% confidence interval (CI), 1.60-2.00] for the first 2 measures in all patients and 1.73 mg/L [95% CI, 1.59-1.89] for all values in all patients). Within-patient variance of IL-6 was also marked (2.69 pg/mL [95% CI, 2.29-3.18]). In group 1, when the 8 CRP values, taken over 10 months, were examined in the low-risk (<1 mg/L), the average-risk (1-3 mg/L), and the high-risk (> 3 mg/L) ranges, the values of 6 patients (40%) remained in the same range for all measurements, those of 7 patients (47%) were in 2 risk ranges, and those of 2 patients (13%) were spread over the 3 risk ranges. Similarly, in group 5, over 9 weeks, 5 patients (42%) had their 3 values in the same range, those of 6 patients (50%) were in 2 ranges, and 1 patient had a value in each of the 3 ranges. The 2 CRP values of groups 2, 3, and 4 had moderate to low correlations, with 36%, 29%, and 9%, respectively, of the second CRP measurement accounted for by the first. In groups 3 and 4, adjustment for changes over time in body mass index, low-density lipoprotein cholesterol levels, smoking status, and medications that could affect CRP (Table), and adjustment for the occurrence of acute coronary events that occurred between the CRP sampling times in 6 patients of group 3, did not modify the fundamental pattern of variability.