Blood Test During Period: How Your Menstrual Cycle Can Affect Blood Test Results

Understand the role of menstrual phases in blood tests, specifically during periods. Learn how sex hormone variations influence the accuracy of results.

Inside Tracker icon
By Staff Writer
Jovan Mijailovic
Edited by Jovan Mijailovic

Updated July 11, 2024.

A woman sitting at a table with a child on her lap.

Sex hormones fluctuate substantially throughout the menstrual cycle, but does it also affect other blood biomarkers?

Research shows that many of them—including those in your lipid, inflammation, and iron groups—vary according to your period. [1] These variations can influence how you interpret your blood test results.

In general, you should schedule a blood draw at the same point in your cycle each time for consistent comparisons. Below, we explore why a regular cycle is important and how best to perform blood testing on your period.

» Schedule a blood draw at a Quest Diagnostics lab and optimize your biomarkers

Key takeaways

  • We always recommend you do a blood test at the same point in a woman's menstrual cycle for consistent comparisons. [1] 
  • If you have a regular menstrual cycle and are focusing on hormone and reproductive health, we recommend you get a blood test during the second half of your cycle. If you're irregular or are on contraceptives, you can test at any point. 
  • Cholesterol levels are more likely to be stable during your period. This is particularly true if your lipid profile is of concern.
  • Vitamin D levels fluctuate throughout the menstrual cycle. Testing in the same phase each time will show consistent results. Vitamin D3 supplementation may also help relieve symptoms.
  • Elevated hs-CRP levels are associated with PMS. If you're affected by it, you may benefit from an anti-inflammatory diet and lifestyle interventions.
  • Overall, evidence shows that specific markers of oxidative stress, inflammation, and cholesterol vary across the menstrual cycle in premenopausal women who are regular. [2]

Phases of the menstrual cycle

There are distinct phases of the menstrual cycle that affect the interplay of hormones within a woman's body, influencing various aspects of her physical and emotional well-being. Below, you can see each one:

1. Menstrual phase

First comes the menstrual phase. A woman gets her period, and her levels of the hormones estrogen and progesterone drop. The process usually lasts 3–7 days, but it can vary individually.

» Explore the relationship between TSH levels and the menstrual cycle

2. Follicular phase

The follicular stage starts soon after. It spans from day one until ovulation—around 16 days. During this time, the pituitary gland releases follicle-stimulating hormone (FSH), signaling the ovaries to prepare to release the ovum (egg)—triggering ovulation.

» Check out more biomarkers you can measure with InsideTracker

3. Ovulation phase

Throughout ovulation, estrogen levels peak and trigger a spike in luteinizing hormone (LH). It then stimulates the release of a mature egg from the ovary. One sign that can help you determine if you're in this phase is a slight rise in body temperature, which happens around day 14 of your cycle.

Can I take a pregnancy test while on my period?

While a period is a good indication that you're not pregnant, a pregnancy test can still be helpful if you are concerned. But, it might not be the most accurate during this time.

It detects a hormone called human chorionic gonadotropin, which is produced by the developing placenta. It takes time for your body to make enough of it for detection, which is typically around the time of a missed period.

» Check out the key biomarkers associated with female fertility

4. Luteal phase

Finally, the luteal phase boosts estrogen and progesterone. Soon after this spike, both hormones drop, and the cycle restarts (barring pregnancy). This stage lasts 11–17 days. It causes women to have PMS symptoms like bloating, headache, weight changes, food cravings, and trouble sleeping.

» Learn how to optimize your hormones for weight loss

The phases of the menstrual cycle.

Importance of a regular menstrual cycle

Each of these phases contributes to what's characterized as a regular cycle. It's an indicator that a woman’s body is working correctly and is ready for pregnancy. Even if having a child isn't in your short or long-term goals, this factor is critical for overall health, as irregularities are associated with:

How hormonal contraceptives affect results

Using hormonal birth control options does change how your hormone levels shift through the menstrual cycle, and their use also impacts other blood biomarkers as well.

» Learn how birth control affects your health and hormones

How does the menstrual cycle affect blood biomarkers?

Some of the biomarkers included in InsideTracker blood tests can be impacted differently based on the menstrual phase a woman is in at the time of the blood draw. Here’s what it means for your results.


Estradiol is the most potent form of estrogen and is the most prevalent during a woman's reproductive years. This hormone fluctuates cyclically during the four phases of the menstrual cycle.

Levels are the lowest during menstruation, peak during ovulation, and then plateau in the luteal phase. Women on contraceptives prevent the steep increase of estradiol during the luteal phase, so its levels remain more stable.

» Learn how to balance testosterone and estrogen to improve your well-being

Abnormally low levels lead to irregular periods, mood changes, and sleeping difficulties. On the other hand, exceedingly high may lead to heavier and more frequent periods, worsened PMS symptoms, and fatigue. Both of these scenarios can also hurt your sex drive. 

The takeaway: You can expect lower estradiol levels if you do a blood test during menstruation. It typically lasts the first five or so days.

» Check out key blood test insights you can't ignore


Progesterone is a steroid hormone that regulates menstruation. Its levels peak during the luteal phase, thickening the uterine lining in preparation so that an egg can attach to it. If you're using contraceptives, you're going to curb this increase, and it'll remain stable throughout the cycle.

» Check out the 9 biomarkers birth control affects

Estradiol declines sharply in the absence of a pregnancy. Additionally, exceedingly high or low progesterone levels impact the frequency and duration of periods. Both extremes may have cognitive effects, like susceptibility to worrying and brain fog

The takeaway: If you're blood testing during your period, you can expect progesterone levels to be lower than if you were to do so during the luteal phase

A graph showing the estradiol and progesterone fluctuations during a normal period cycle.


Conventional wisdom—and many studies—tell us that blood loss during menstruation is the primary cause of lower iron levels in women. Here's why:

  • Typically, women lose about 16mg of iron for the average menstrual period, though it can be as high as 36mg or above for women with menorrhagia—clinical excessive menstruation.
  • If we consider that average iron levels in females tend to be 3,000-4,000 mg, it means you'd lose about 0.4–0.5% of the total amount in your body. But this seemingly negligible amount can impact markers of iron status in healthy, menstruating women. 

» Find out how inflammation affects your iron levels

There's evidence from studies that menstruation affects biomarker levels in menstruating women. Hemoglobin, ferritin, and percent transferrin saturation are usually lower in samples collected from females during the luteal phase of the cycle. [3] In other words, your iron status can be lower if you do a blood test during a period.

At the same time, there are implications from other research that conflict with this conclusion. It says that the menstrual cycle doesn't affect the above clinical markers in iron-depleted women. [3]

The takeaway: We recommend that premenopausal women get at least 18mg of dietary iron daily to compensate for menstrual blood losses. This is especially the case if you’re in this group of females and exercise regularly and or follow a vegan or vegetarian diet.

» Discover how to optimize your training around your menstrual cycle


Research shows that lipid levels can fluctuate throughout a woman’s menstrual cycle as a normal response to variations in estrogen. [4]

Draper et al. showed significant reductions in total cholesterol, HDL (good) cholesterol, and triglyceride concentrations in the luteal phase relative to the follicular phase.

» Learn how to reduce ApoB cholesterol with food

These findings support previous research on the topic. Additionally, females who were undergoing estradiol treatment—but not progesterone—saw a 30% reduction in triglycerides in the luteal phase. [4]

The takeaway: Due to the known fluctuations in lipid levels, you should test at the same phase of your cycle each month for consistent results. Be careful when interpreting cholesterol and triglyceride blood test results that traverse menstrual cycle phases, and consult a medical professional before jumping to a conclusion.

» Find out if you can lower your cholesterol without statins

Vitamin D

Your period also affects vitamin D. In fact, research has consistently shown that it tends to be higher compared to other phases of the menstrual cycle. [5] Interestingly, there's also evidence that you can improve PMS symptoms with supplementation. [6]

The takeaway: Like other biomarkers, vitamin D levels fluctuate throughout your cycle. If you have PMS and your blood test results show lower levels, a vitamin D3 supplement could help relieve your symptoms.

» Discover all you need to know about vitamin D and sun exposure


A prospective cohort investigated 259 healthy menstruating women ages 18–44 who weren't on oral contraceptives. [7] It showed that levels of hs-CRP varied significantly across the menstrual cycle. Here's how it progressed:

  1. hs-CRP was highest during menstruation
  2. It then decreased steadily throughout the follicular phase
  3. Soon after, it dropped to the lowest level on the day of ovulation
  4. Finally, it increased back to baseline in the luteal phase
Symptoms of PMS observed in the luteal phase were also associated with elevated CRP. [2,4,5]

The takeaway: Levels will fluctuate throughout each phase of the cycle, and you should consider the timing of your hs-CRP blood test when looking at results. If PMS is an issue, focus on an anti-inflammatory diet and lifestyle interventions to relieve symptoms.

» Learn how to measure inflammation and explore it's key markers

Blood tests and fluctuating sex hormone levels

Although sex levels for sex hormones like progesterone and estradiol change significantly during the menstrual cycle, there are established normal ranges. The scope is based on the current phase you're in and whether you use contraceptives.

Normal reference ranges for female sex hormones (premenopause).

» Take your analysis further with an optimal zone for all biomarkers

Time your blood test wisely

Knowing when to schedule a blood test can impact the accuracy of your results. For a clearer picture of your overall health, consider discussing the timing of your blood test with your doctor to ensure it falls outside the window that might be affected by your cycle.

A woman’s period can be a very personal topic. But here at InsideTracker, we strive to provide evidence-based science to empower individuals to take control of their health. That's why we now offer new and improved personal analysis based on your menopause status and the use of exogenous hormones. Intrigued? Click the button below to learn more.


  1. N. Romero-Parra et al., “Influence of the menstrual cycle on blood markers of muscle damage and inflammation following eccentric exercise,” International Journal of Environmental  Research and Public Health/International Journal of Environmental Research and Public Health, vol. 17, no. 5, p. 1618, Mar. 2020, doi: 10.3390/ijerph17051618. Available:
  2. E. F. Schisterman, S. L. Mumford, and L. A. Sjaarda, “Failure to consider the menstrual cycle phase may cause misinterpretation of clinical and research findings of cardiometabolic biomarkers in premenopausal women,” Epidemiologic Reviews, vol. 36, no. 1, pp. 71–82, Sep. 2013, doi: 10.1093/epirev/mxt007. Available:
  3. A. Belza, M. Henriksen, A. K. Ersbøll, S. H. Thilsted, and I. Tetens, “Day-to-day variation in iron-status measures in young iron-deplete women,” British Journal of Nutrition, vol. 94, no. 4, pp. 551–556, Oct. 2005, doi: 10.1079/bjn20051461. Available:
  4. S. L. Mumford, S. Dasharathy, and A. Z. Pollack, “Variations in lipid levels according to menstrual cycle phase: clinical implications,” Clinical Lipidology, vol. 6, no. 2, pp. 225–234, Apr. 2011, doi: 10.2217/clp.11.9. Available:
  5. C. F. Draper et al., “Menstrual cycle rhythmicity: metabolic patterns in healthy women,” Scientific Reports, vol. 8, no. 1, Oct. 2018, doi: 10.1038/s41598-018-32647-0. Available:
  6. A. Arab, S. Golpour-Hamedani, and N. Rafie, “The Association Between Vitamin D and Premenstrual Syndrome: A Systematic Review and Meta-Analysis of Current Literature,” Journal of the American College of Nutrition, vol. 38, no. 7, pp. 648–656, May 2019, doi: 10.1080/07315724.2019.1566036. Available:
  7. E. B. Gold, C. Wells, and M. O. Rasor, “The Association of Inflammation with Premenstrual Symptoms,” Journal of Women’s Health, vol. 25, no. 9, pp. 865–874, Sep. 2016, doi: 10.1089/jwh.2015.5529. Available:

Disclaimer: We acknowledge that not everybody who menstruates identifies as a woman. InsideTracker also doesn't diagnose or treat medical conditions. If you have any health concerns, consult a doctor.