Background: C-reactive protein (CRP) has recently been introduced in cardiovascular medicine as a predictor of myocardial infarction, stroke and peripheral artery disease in different populations. We hypothesized that elevated CRP levels are associated with renal function abnormalities.
Methods: To test this hypothesis, we studied the relationship between CRP levels and renal function loss measured as diminished creatinine clearance in a large non-diabetic population (7317 subjects). In addition, the associations and confounding effects of established renal risk factors that could explain the association between CRP and diminished renal filtration were studied. Also, the association of CRP with early alterations in renal function, such as those evidenced by a relatively high glomerular filtration ("hyperfiltration"), was examined. CRP levels were divided in quartiles. Subjects with CRP levels within the first quartile were defined as the reference group. Diminished renal filtration and hyperfiltration were defined as a creatinine clearance below or exceeding two times the prediction interval of the age- and sex-related reference group.
Results: Elevated CRP levels were positively associated with cardiovascular and renal risk factors: age, body mass index, blood pressure, serum cholesterol level, smoking, plasma glucose level and elevated urinary albumin excretion. Elevated CRP was positively associated with diminished filtration (OR 1.8; 95% CI 1.2 to 2.6). In multivariate analyses, CRP was independently associated with a diminished filtration (OR 1.9; 95% CI 1.3 to 2.9). Interestingly, CRP also was associated with hyperfiltration (highest quartile, OR 1.7; 95% CI 1.2 to 2.5). However, body mass index accounted for most of the relationship between CRP and hyperfiltration.
Conclusions: As in cardiovascular disease, CRP appears to be a risk marker for renal function loss. The mechanism of this relationship remains to be clarified. However, the association between CRP, body weight, and a relatively elevated creatinine clearance is a hypothesis-generating finding, suggesting that early inflammatory processes related to high body fat may predispose the kidney to glomerular hyperfiltration-related renal function loss.