May 29, 2025
Can You Do a Blood Test During Your Period? Why Timing Matters
Why timing blood tests for women matters more than you think.
Written by
Mito Team
For women, their bodies aren’t the same every day of the month—and that includes their blood. If you’ve ever wondered whether you can take blood tests during periods or if that's a bad time, you’re not alone.
The short answer? You can—but timing can seriously affect your results. Let’s break it down.
What Happens During Your Menstrual Cycle
The menstrual cycle typically lasts 21 to 35 days and has four main phases:
1. Menstrual Phase (Days 1 to 7): This is when your period starts. Hormones like estrogen and progesterone are at their lowest, and you're losing blood, which might affect your iron levels.
2. Follicular Phase (Days 1 to 14): After your period, estrogen rises. This phase is good for checking things like blood sugar, insulin, and cholesterol levels.
3. Ovulation (~Day 14): Around the middle of your cycle, there's a spike in luteinizing hormone (LH) that triggers an egg to be released.
4. Luteal Phase (Days 15 to 28): In this phase, progesterone increases. You might notice that you feel a bit bloated, tired, or moody. Some markers of inflammation can go up as well.
Each of these phases involves hormone changes that can even affect health markers, including things like liver enzymes and cholesterol.
Can You Do a Blood Test During Your Period?
Yes, you can get a blood test during your period, but whether you should depends on what you’re testing for and why. Menstruation is completely normal, but it does bring some changes that can affect your blood test results.
Here’s what might be affected:
Iron Levels
Since you're actively losing blood during your period, your iron levels, such as hemoglobin, ferritin, and transferrin saturation, might be lower than usual. Getting an iron blood test while on your period could make it look like you have an iron deficiency, especially if your periods are heavy.
For the most accurate results of your iron status, it’s often better to wait until midway through your cycle, when your iron levels are more stable.
Inflammation markers
High-Sensitivity CRP (C-reactive protein) is a marker of inflammation that often spikes during menstruation because of your body’s normal response during shedding of the uterine lining. This spike might lead to confusing results if you’re testing for chronic inflammation.
Unless your doctor is looking at inflammation related to your period, it’s generally better to wait until after your menstruation to do a blood test.
Hormone levels
Your period marks the start of a new menstrual cycle. On the first day, your hormone levels, like estrogen and progesterone, are at their lowest. This is a good time for hormone blood tests, especially if you’re checking for fertility or reproductive health. That includes testing Follicle Stimulating Hormone (FSH), Luteinizing Hormone (LH), and estradiol, which can give insight into ovarian function and fertility.
But if you're not specifically doing fertility or reproductive hormone testing, a hormone blood test during your period might not be the best time to check for other blood markers that are sensitive to hormonal fluctuations.
Lipid profile
Your cholesterol levels vary throughout your cycle. Total cholesterol, LDL, HDL, and triglycerides usually peak after your period ends.
Testing during your period might not give you the most accurate cholesterol results. If you're monitoring cholesterol, it’s best to have tests done at the same point in your cycle for clear comparisons.
Related: Managing High Cholesterol During Period Effectively: Causes, Symptoms & Solutions
So, while it's safe to have a period blood test, the timing affects the results. If you’re unsure, it’s a good idea to chat with your doctor, or you could look into blood testing services like Mito Health that consider your cycle phase when interpreting results.
Best Timing for Different Blood Tests During Period
Test Type | Best Phase to Test | Why It Matters |
Reproductive Hormones (FSH, LH, Estradiol) | Early follicular (Day 3) | Shows baseline hormone production |
Progesterone | Mid-luteal (~Day 21) | Confirms ovulation |
Iron (Hemoglobin, Ferritin) | Mid-cycle | Avoid drop in levels from menstrual blood loss |
Lipid Panel (Cholesterol, Triglycerides) | Same point each cycle (e.g., follicular) | Ensures consistent readings |
CRP (Inflammation) | Not during menstruation | Avoids falsely high results |
Thyroid Hormones (TSH, T3, T4) | Same cycle phase every time | TSH can rise around ovulation |
Glucose/Insulin | Track across phases | Insulin resistance may rise in the luteal phase |
Want to confirm ovulation before doing a luteal phase blood test? Try using an ovulation test right before your period. This helps ensure you're testing at the right time.
Can Period Blood Affect a Urine Test?
Yes. Menstrual blood can enter the urine stream and contaminate a urine test, especially if collected mid-flow. That can cause red blood cells or protein in your result, potentially mimicking a UTI. That’s why it’s important for healthcare providers to ask if you’re menstruating when doing a urinalysis.
What If You Have an Irregular Cycle or Take Birth Control?
Not every woman has a textbook 28-day cycle. If yours is irregular, it’s best to track ovulation using a thermometer or an at-home LH test. Work with your provider to schedule tests based on your unique cycle, not just the calendar.
When you’re on hormonal birth control, your natural cycle is suppressed, which flattens hormone fluctuations. You can usually test at any time, but it’s important to tell your healthcare provider you’re on contraceptives, which affect hormones, cholesterol, and more.
Know Your Cycle, Time Your Tests
Your menstrual cycle influences your mood and energy, and it also affects your bloodwork. While it’s perfectly safe to do a blood test during your period, the timing changes how certain results look and how they’re interpreted.
Whether you’re testing hormones, iron, cholesterol, inflammation, or thyroid function, understanding where you are in your cycle helps you and your healthcare provider get a more accurate picture of your health.
You can schedule your next blood test with Mito Health based on your cycle, symptoms, and health goals, so your results are meaningful and not misleading.