When to Test Hormones: A Cycle-Day Guide for Blood Tests in Bangkok

Hormone testing guide · 2026

Half of all confusing hormone results are timing errors. This is the reference page to check before you book the draw.

By MedEx · Updated September 2026 · Approx. 7-minute read

Quick answer

Hormone results are only interpretable against a reference range built for the same conditions the sample was taken in. Three variables decide that: time of day (testosterone, cortisol and 17-hydroxyprogesterone must be morning), menstrual cycle day (FSH, LH and estradiol on day 2–4; progesterone seven days before the next expected period), and current medication (hormonal contraception, HRT, steroids and biotin all distort results). Everything else — AMH, DHEA-S, TSH, prolactin, SHBG, IGF-1 — can be drawn on any day.

In this guide

1. The full timing table
2. How to count your cycle day correctly
3. When cycles are irregular, absent, or you are on contraception
4. Other things that shift results

The full timing table

How to count your cycle day correctly

Day 1 is the first day of full menstrual flow. Light spotting the day before does not count as day 1, and this single detail causes a meaningful share of mistimed day-3 draws.

For the mid-luteal progesterone, count backwards. The luteal phase is relatively fixed at around 14 days, while the follicular phase varies — so seven days before the next expected period is far more reliable than a fixed day 21.

If your cycles vary by more than three or four days, note the range and tell the booking team. At-home collection through the MedEx lab test catalogue makes it much easier to hit a specific day without rearranging work.

When cycles are irregular, absent, or you are on contraception

Irregular cycles. Day-specific timing may be impossible. Clinicians often draw a full panel on any day and interpret with that limitation stated, or use home LH kits to time a progesterone draw.

Absent periods. The priority shifts to finding the cause: pregnancy test, TSH, free T4, prolactin, then FSH, LH, estradiol, testosterone, SHBG and DHEA-S. Cycle timing becomes irrelevant.

On hormonal contraception. Combined contraception suppresses FSH, LH and endogenous estradiol, raises SHBG and lowers androgens. Results reflect the medication, not your physiology. Where testing matters, a washout period may be advised — discuss it with a clinician rather than stopping contraception unplanned.

After hysterectomy without oophorectomy. Cycle tracking is impossible, so timing is guided differently. Mention this at booking.

Other things that shift results

• Acute illness or fever — testosterone, IGF-1 and thyroid results are all distorted. Wait until you are well.
• Poor sleep or night shifts — the cortisol and testosterone rhythms move with your sleep schedule, not the clock. Tell the clinician your actual pattern.
• Strenuous exercise before the draw — raises prolactin and cortisol.
• High-dose biotin supplements — can badly distort thyroid and other immunoassays.
• Recent contrast imaging with iodine — affects thyroid testing.
• Steroids in any form, including inhaled and topical — suppress the cortisol axis.

When in doubt, ask before booking rather than repeating the test afterwards. See the hormone panel selection guide for which markers to order in the first place.

Frequently asked questions

What counts as day 1 of my cycle?

The first day of full menstrual flow. Light spotting the day before does not count, and this is a common cause of mistimed day-3 blood tests.

Which hormones must be tested in the morning?

Total testosterone, serum cortisol and 17-hydroxyprogesterone. All three have a strong daily rhythm and should be drawn between roughly 8am and 10am.

Which hormones can be tested on any day?

AMH, DHEA-S, TSH, free T4, prolactin, SHBG and IGF-1 can all be drawn on any cycle day without fasting.

How do I time a progesterone test with a long cycle?

Count backwards seven days from your expected next period. In a 35-day cycle that is day 28, not day 21.

Can I test hormones while on the contraceptive pill?

Results will reflect the medication rather than your own physiology, since combined contraception suppresses FSH, LH and estradiol while raising SHBG. Discuss a washout period with a clinician instead of stopping contraception unplanned.

Does illness affect hormone results?

Yes. Acute illness and fever distort testosterone, IGF-1 and thyroid results. Wait until you have recovered before testing.

Sources and further reading

1. MedEx lab test catalogue
2. NICE guideline CG156: Fertility problems
3. MedEx functional lab tests

Medical disclaimer: This article is general health information and does not replace medical advice, diagnosis or treatment. Laboratory reference ranges differ between laboratories and results must be interpreted alongside your symptoms, medicines and medical history. Speak with a qualified clinician before starting, stopping or changing any treatment. Service details, inclusions and prices can change — confirm them with MedEx before booking.