When Should I do a Hormone Blood Test for Accurate Results?

When it comes to assessing hormone levels, a blood test is a great place to start. It’s an inexpensive test and, if timed properly, can be a really useful tool.

Although inexpensive, I wouldn’t say it’s non-invasive, especially if you’re anything like me and not a huge fan of needles or the sight of your own blood. Yes, I know, how can a women’s health specialist be squeamish about blood? Don’t worry, it’s only my own blood that makes me go all wobbly at the knees. Don’t ask me why- it’s a thing… and it’s not uncommon.

It’s for this reason that it really gets my goat when women come into my clinic with blood test results from their GP, only for me to find out they were done on the wrong day of their cycle. It’s a huge waste of time, and of course, an unnecessary visit for a dreaded blood test.

Testing hormones at the wrong time can lead to inaccurate results, making them difficult to interpret. To get the most reliable insights, it’s essential to know when and how to test your hormones properly.

In this guide, we’ll cover the best timing for key hormone tests, preparation tips, and common pitfalls to avoid, so your results are both accurate and actionable.

Why Timing Matters in Hormone Blood Testing

Hormones fluctuate naturally throughout the day and across your menstrual cycle. Many follow a diurnal rhythm, meaning their levels rise and fall depending on the time of day. Others vary dramatically based on your cycle phase. For example, reproductive hormones like FSH, LH, and Oestradiol are best tested at the start of your cycle, while Progesterone needs to be tested after ovulation.

Testing at the wrong time can produce misleading results, potentially leading to misdiagnosis or ineffective treatment plans. That’s why correct timing, alongside proper preparation, is important for reliable hormone testing.

General Guidelines for Hormone Testing

Test in the Morning, Fasted

For most hormones, testing first thing in the morning while fasted (no food or drink except water) provides the most consistent baseline. Avoid eating, drinking coffee, exercising, or sexual activity on the morning of your test, as these can affect hormone levels. For adrenal hormones like Cortisol and Prolactin, it’s also best to avoid these activities the night before.

These hormone testing guidelines are important for both men and women. While men don’t need to consider monthly cycle timing, their hormones do follow a diurnal rhythm, meaning levels fluctuate throughout the day. For this reason, men should also aim to test their hormones early in the morning, ideally between 6–9 AM, to capture the most accurate baseline.

Key Hormones and When to Test Them

FSH, LH, and Oestradiol

These hormones provide important information about ovarian function and menstrual cycle health and are essential for sperm production in men.

• When to test: Day 2 or 3 of your menstrual cycle.

• Note: Day 1 is the first full day of bleeding (spotting does not count)

  
  

FSH and LH follow a diurnal, pulsatile pattern, which is why it’s essential to test them first thing in the morning to capture accurate baseline levels. These hormones provide valuable insight into the function of the Hypothalamic-Pituitary-Ovarian (HPO) axis, helping us understand how well the early part of your cycle is functioning in preparation for ovulation. FSH and LH work closely with Oestrogen and Progesterone, influencing their production and regulation.

Oestradiol, a form of estrogen, can also be tested in the luteal phase, alongside Progesterone. Its levels not only reflect ovulatory function but also give us a window into endometrial health, since oestrogen is responsible for thickening the uterine lining during the follicular phase.

As with all hormones, we’re looking for a balance, not too high or too low. There’s a hormonal "sweet spot," and interpreting oestrogen levels in isolation won’t give the full picture. It’s crucial to assess them in context, particularly alongside progesterone, to gain a more accurate understanding of overall cycle health.

Progesterone

Often tested to confirm ovulation and evaluate luteal phase function, also very important for embryo implantation and pregnancy.

• When to test: 7 days after ovulation - this is when this hormone should peak.

• Since cycle lengths vary, it’s important to track your ovulation first (using basal body temperature, ovulation kits, and cervical mucus monitoring) to time this test correctly.

  
  

Important: Many doctors order a “Day 21 Progesterone” test routinely, but this timing is only accurate for women with a textbook 28-day cycle who have ovulated on day 14 - ovulation timing will vary from women to women. Personalised timing is essential for reliable results.

Testing progesterone at the start of the menstrual cycle is useless as progesterone is produced after ovulation from the corpus luteum (a glandular structure formed from the ruptured follicle where the egg is released).

P4:E2 Ratio (Progesterone to Oestradiol)

Testing both Progesterone and Oestradiol 7 days after ovulation can help detect issues like luteal phase deficiency, Oestrogen excess or hormonal imbalances common in perimenopause.

Prolactin

Prolactin is a hormone involved in reproductive health and can affect menstrual cycles and fertility if elevated.

• When to test: Cycle day 2 or 3 or peak luteal phase so 7 days after ovulation.

• Timing and Preparation: Prolactin levels can be influenced by stress, physical activity, and sexual activity. For accurate results, test first thing in the morning, fasted, and avoid exercise, sexual activity, and caffeine the night before and the morning of your test.

  
  

Thyroid Hormones: TSH, Free T4, and Free T3

Your thyroid plays a central role in regulating metabolism, energy levels, and overall hormonal balance, but its influence doesn’t stop there. It also impacts heart rate, bone health, circulation, and has a significant effect on both physical and mental wellbeing. What’s more, thyroid function is closely interconnected with other hormones, and can be particularly sensitive to prolonged periods of stress.

• When to test: Any day of the month

• Preparation: Avoid biotin supplements or multivitamins for at least 5 days prior, as biotin can interfere with thyroid test results.

  
  

Testosterone, DHEA, and Cortisol

These hormones play a key role in energy, stress response, libido, and overall vitality. Testosterone is essential for both sexes, supporting ovulation in women and sperm production and quality in men. DHEA and Cortisol are adrenal hormones, and while they’re often misunderstood, they’re vital to health. DHEA is actually a precursor to our sex hormones, while Cortisol, despite its bad reputation, is critical for survival, influencing everything from metabolism to immune function and blood pressure regulation.

• When to test: Any day of the month but if you are testing a full hormone profile I find it best to do them at the same as this makes it easier to interpret - plus less blood tests for you.

• Timing: First thing in the morning, fasted (6–9 AM)

• Preparation: Avoid coffee, physical exercise, and sexual activity the night before and morning of your test, as these can spike hormone levels and affect accuracy.

  
  

SHBG

SHBG (Sex Hormone Binding Globulin) is a protein produced by the liver. Think of it as the big sister of your hormones, its job is to bind to hormones like estrogen and testosterone, carrying them through the bloodstream and keeping their levels in check by rendering them inactive when necessary. I like to include SHBG in hormone blood panels because it offers valuable insight into hormone bioavailability, that is, how much hormone is actually free and active in the body. It can also flag potential issues with blood sugar regulation, adding another layer of depth to your overall hormonal picture.

• When to test: Cycle day 2 or 3 or peak luteal phase, 7 days after ovulation.

  
  

Preparing for Your Hormone Blood Test: Tips to Ensure Accuracy

• Avoid supplements that can interfere with results (like biotin) for 5-7 days before testing unless prescribed by your doctor.

• Avoid sexual activity, exercise, and caffeine the night before and morning of your test.

• Track your menstrual cycle carefully to schedule tests like FSH, LH, Oestradiol, and Progesterone on the correct days.

  
  

Final Thoughts: Accurate Hormone Testing Empowers Better Health Decisions

When testing your hormones, timing is everything. By scheduling your tests according to your cycle and following preparation guidelines, you ensure your results reflect your true hormonal status. Accurate data allows healthcare providers to make informed recommendations tailored to your unique needs, whether you're managing fertility, balancing hormones, or navigating perimenopause.

As part of my investigation process I will often recommend a comprehensive blood test. If you would like support deciding on the right blood tests for your needs, ascertaining when in your cycle you need to do these tests and clinical interpretation of the results please get in touch.

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