Blood Tests for Irregular Periods: Which Hormone Test to Book and When

Irregular periods are common and have many possible causes. Stress, weight changes, polycystic ovary syndrome (PCOS), thyroid problems, raised prolactin, perimenopause and pregnancy can all affect your cycle. A female hormone test, sometimes called a hormone test for women, can help narrow down the cause, but only if it’s taken on the right day.

Some symptoms need a GP appointment rather than a private test. See your GP first if you have:

• sudden, very heavy bleeding;
• bleeding after sex or between periods;
• any bleeding after the menopause;
• severe pelvic pain.

Which hormones are usually checked

Blood tests for irregular periods usually focus on a small group of hormones. Each one answers a different question:

• FSH and LH. These control the cycle. The balance between them can be part of the picture in PCOS, and a raised FSH can point to reduced ovarian function.
• Oestradiol. This is the main form of oestrogen, and it rises and falls through the cycle.
• Prolactin. A raised level can stop periods or make them irregular.
• Testosterone and SHBG. These are relevant to PCOS symptoms such as acne or excess hair growth.
• Thyroid function (TSH). Both an underactive and an overactive thyroid can disrupt the cycle.

Swift’s Female Hormone blood test costs £65. The product page lists every marker included, so check it against your symptoms. Thyroid function can be checked with a separate thyroid test if you want it covered as well.

When in your cycle to book

Timing is the most common reason hormone results are hard to interpret. Use this as a guide:

Marker	Usual timing
FSH, LH and oestradiol	Days 2 to 5 of your period
Progesterone (ovulation check)	About 7 days before your next expected period
Prolactin, testosterone and thyroid	Any day; a morning appointment is helpful
No periods at all	Any day, after taking a pregnancy test

Day 1 is the first day of full bleeding, not spotting. If your cycles are very irregular, aim for days 2 to 5 of the next bleed you have.

Hormonal contraception changes these results because it suppresses your natural cycle. Tell the clinician if you use it, and don’t stop prescribed contraception without medical advice.

Which test suits you?

Your symptoms point to the most useful test:

• Irregular cycles with acne or unwanted hair: book a female hormone test and consider a thyroid test.
• Wanting to understand your egg reserve: an AMH blood test, which can be taken on any day.
• Over 45 with hot flushes and changing periods: NICE says menopause is usually diagnosed on symptoms alone. Our guide to the menopause blood test under 45 explains when testing helps.
• Heavy periods and tiredness: an iron blood test may matter more than hormones.

PCOS blood test: what it can show

There’s no single PCOS blood test. Instead, doctors look at a group of results alongside your symptoms. Blood tests can show raised testosterone or free androgen index, and an LH and FSH pattern that sometimes points towards PCOS. They also help rule out other causes of irregular periods, such as thyroid problems or raised prolactin.

PCOS is usually diagnosed when two of three features are present: irregular or absent ovulation, signs of raised androgens in your symptoms or blood results, and polycystic ovaries on an ultrasound scan. A blood test is a useful first step towards that conversation with your GP.

What results can and can’t tell you

Hormone results are one piece of the picture, not a diagnosis on their own:

• PCOS is diagnosed using your cycle history, symptoms, blood results and sometimes an ultrasound scan.
• Hormone levels change from cycle to cycle, so a single result may need repeating.
• Normal results don’t mean your symptoms aren’t real. They help rule some causes in or out.

Take your results to your GP, who can look at them alongside your history.

Clinic or home collection

Getting a test on days 2 to 5 can be tricky around work and family. A home visit makes cycle-timed testing easier, while clinic appointments suit people with predictable schedules. Swift has clinics across Essex, plus Bromley and Sunbury, and offers home visits across Essex, Bromley and Surrey. Use the clinic finder to see what’s near you.

How booking works

1. Work out which cycle day you need.
2. Choose the Female Hormone blood test online.
3. Book a clinic or home appointment for that day.
4. Receive your results and share them with your GP.

Keeping a cycle diary

Before you test, keep a simple record of when each period starts and ends, how heavy it is and any symptoms. Two or three months of notes make it much easier to pick the right test day, and they give your GP useful context when you share your results.

Frequently asked questions

What blood tests are done for irregular periods?

Commonly FSH, LH, oestradiol, prolactin, testosterone and thyroid function, chosen according to your symptoms.

What day should I have a female hormone blood test?

Usually days 2 to 5 for FSH, LH and oestradiol. Progesterone is taken about seven days before your next expected period.

Can I test if I have no periods?

Yes. Rule out pregnancy first. Testing can then be done on any day.

Does the pill affect hormone results?

Yes. Hormonal contraception suppresses natural hormone levels, so results may not reflect your own cycle.

Can a blood test diagnose PCOS?

Not on its own. Diagnosis also considers your cycle history and symptoms, and sometimes an ultrasound.

Is there a female hormone test near me?

Swift has clinics across Essex, plus Bromley and Sunbury, and offers home visits in covered areas.

Book your hormone test

If you want answers about irregular periods, book Swift’s Female Hormone blood test and choose a cycle-timed appointment.