Body weight and oral contraceptives are the most important modulators of serum CRP levels.

Background: C-reactive protein (CRP) levels are modulated by endogenous and exogenous factors independently of inflammation. The present study investigated the impact of oral contraceptives, endogenous oestrogens, age, gender, smoking, body mass index (BMI) and lipid levels on CRP concentrations in a healthy collective.

Methods: Highly sensitive CRP, total cholesterol, HDL-cholesterol and LDL-cholesterol levels were measured in 850 blood donors (438 M, 412 F); 227 women in this group used oral contraceptive formulations (OC). Additionally, serum samples from 58 women undergoing in vitro fertilization cycles (IVF) were tested for CRP. Results. The 97.5th percentile of CRP levels of the blood donors was 4.91 mg/L in men, 7.52 mg/L in OC non-users and 11.95 mg/L in OC users. Overweight gives a 2-fold increase of median CRP levels in men and women. The combination of overweight and OC use in women resulted in 6-fold median CRP levels. Age, smoking and lipid levels were influencing factors of lower significance. In IVF patients the elevated oestradiol levels had no influence on CRP concentrations in multivariance analysis.

Conclusion: The diagnostic and predictive value of CRP levels is most affected by BMI and oral contraceptive use, which suggests the need for further investigations into the role of CRP modulating factors in monitoring infectious diseases.