Are monocytes (mononuclear white blood cells) elevated during menstruation?

Monocyte Levels During Menstruation

Monocyte levels can increase during menstruation, particularly in the post-ovulatory and menstrual phases of the cycle, as part of the normal inflammatory response associated with endometrial breakdown and repair.

Normal Monocyte Levels and Menstrual Cycle Changes

• Normal monocyte percentages typically range from 4-10% of total white blood cells 1
• Monocyte counts show cyclical variations during the menstrual cycle, with increases observed during menstruation in some women 2
• One detailed study following a woman through eight consecutive menstrual cycles showed variations in monocyte counts that followed a pattern similar to neutrophil counts throughout the cycle 2

Physiological Mechanisms

• The increase in monocytes during menstruation appears to be part of the inflammatory-like response that occurs during endometrial breakdown and repair 3
• Post-ovulation, there is a significant increase in the intrinsic production of pro-inflammatory cytokines (IL-1α, IL-1β, and TNF-α) by monocytes, suggesting prior activation in vivo 3
• This activation is likely related to hormonal changes, as studies have shown that:
  • Progesterone withdrawal results in significant increases in inflammatory factors in endometrial stromal cells 4
  • Cortisol significantly increases inflammatory factors in endometrial endothelial cells 4
  • Estrogen levels fluctuate significantly during the menstrual cycle, with approximately ten-fold changes in estradiol 5

Clinical Significance

• The increase in monocytes during menstruation is generally considered a normal physiological response and not clinically significant in most cases 1
• Monocyte elevation during menstruation contributes to efficient endometrial repair after menses 4
• Women with heavy menstrual bleeding have shown reduced levels of certain monocyte-related factors (such as CXCL4) in endothelial cells during menstruation compared to women with normal menstrual bleeding, suggesting a potential role in menstrual disorders 4

Interpretation Considerations

• When interpreting CBC results in women of reproductive age, clinicians should consider the timing within the menstrual cycle 6
• A single elevated monocyte percentage should not be over-interpreted without clinical context 1
• For accurate assessment, it's helpful to know:
  • The day of the menstrual cycle when blood was drawn 6
  • Whether the patient uses hormonal contraceptives, as these can affect menstrual blood loss and subsequent hematological parameters 5, 6
  • The presence of any symptoms suggesting infection or inflammation 1

Monitoring and Follow-up

• For patients with elevated monocyte percentages, serial measurements may be more informative than a single value 1
• Correlation with clinical symptoms and other laboratory findings is essential 1
• Persistent monocytosis (>1×10^9/L) for ≥3 months without clear reactive cause warrants referral to a hematologist 7