Preanalytic Variability

Physiological and Clinical

Age, gender, and ethnicity. Although most studies have shown no relationship between age and serum CRP concentration (7,14) (Fig. 2), at least two studies have reported a slight increase in CRP concentrations with age (15,16). This increase might be owing to the higher incidence of obesity that is associated with aging (15). In the Women's Health Study that included 15,770 participants, only a slight association of CRP with age was seen: median CRP concentrations for individuals 45-54, 55-64, 65-74, and ©75 yr of age were 1.31, 1.89, 1.99, and 1.52 mg/L, respectively (17).

The availability of hsCRP assays has enabled the determination of population distributions ofthis protein. Several studies have shown that the distribution ofCRP concentrations in both genders was non-Gaussian when evaluated for skewness and kurtosis (7,14) (Fig. 3). The AHA/CDC-proposed cut points correspond to the approximate tertiles of CRP distribution. Findings from American and European studies have shown comparable distributions of CRP concentrations among men and women not receiving hormone replacement therapy (HRT) (17-19) (Table 1). As indicated earlier, the 50th percentile of CRP is about 1.5 mg/L for both genders. Furthermore, data from the National Health and Nutrition Examination Survey III showed no significant difference in the distribution of CRP concentration among white, African American, and Mexican American men (18,19) (Table 2). Moreover, a comparable CRP distribution was seen in Japanese men (20) but not in Japanese women, who have a slightly lower CRP concentration. By contrast, other

Log CRP

Fig. 3. Combined distribution of CRP values from different population studies. (Courtesy ofDr. Gary Myers of the CDC.)

Table 1

Population Distributions of CRP (mg/L)a

Percentile

Table 1

Population Distributions of CRP (mg/L)a

Percentile

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