CRP at early follicular phase of menstrual cycle can cause misinterpretation for cardiovascular risk assessment.

Objective: C-reactive protein (CRP) is a well-known marker of inflammation and infection in clinical practice. This study is designed to evaluate CRP levels in different phases of menstrual cycle, which might end up with misleading conclusions especially when used for cardiovascular risk assessment.

Methods: Twenty-seven women were eligible for the cross-sectional study. Venous blood samples from each participant were collected twice during the menstrual cycle. The first sampling was held at 2nd to 5th days of the menstrual cycle for FSH, estradiol, CRP, and sedimentation, and the second was done at 21st to 24th days of the menstrual cycle for measurement of progesterone, CRP, and sedimentation values.

Results: CRP values were significantly higher in the early follicular phase compared to luteal phase (1.8 mg/L [0.3-7.67] vs. 0.7 mg/L [0.1-8.3], p < 0.001, respectively). In both phases of the menstrual cycle, sedimentation rate was similar (12.1 ± 6.7 vs. 12.3 ± 7.7; p = 0.717, respectively).

Conclusions: CRP levels in early follicular phase of the menstrual cycle (menstruation) are significantly higher than CRP levels in luteal phase of the same cycle. In reproductive age women, detection of CRP for cardiovascular risk assessment during menstruation might not be appropriate.