Could It Be PCOS? The Signs and Blood Tests That Help

Polycystic ovary syndrome (PCOS) is one of the most common hormone conditions in women of reproductive age, yet it's often diagnosed late. It can affect periods, skin, hair, weight and fertility — and because the signs vary so much from person to person, many women spend years wondering what's going on. Here's what PCOS is and how blood tests help build the picture.

What is PCOS?

Despite the name, PCOS isn't really about cysts — it's a hormonal condition. Doctors commonly use the Rotterdam criteria, which look for at least two of these three features:

• Irregular or absent periods (a sign that ovulation isn't happening regularly)
• Raised androgens ("male-type" hormones) — either on a blood test or from signs like acne and excess hair
• Polycystic-appearing ovaries on an ultrasound scan

Crucially, PCOS is a clinical diagnosis. No single blood test confirms it — the results are interpreted alongside your symptoms and, where needed, a scan.

Common signs

• Irregular, infrequent or missing periods
• Persistent acne and oily skin
• Excess hair on the face, chest or abdomen (hirsutism)
• Thinning hair on the scalp
• Weight gain or difficulty losing weight
• Difficulty conceiving

The hormone panel that helps

A PCOS hormone panel typically measures total testosterone, SHBG and the free androgen index (FAI) to assess androgen levels, along with LH, FSH, oestradiol, progesterone and prolactin to look at the wider hormonal balance. In PCOS, testosterone and the FAI are often raised, and LH may be high relative to FSH. Because hormone levels shift across the cycle, testing is often timed to days 2–5 where possible, with progesterone around day 21 to check whether ovulation is occurring.

Ruling out other causes first

Several other conditions can cause irregular periods or raised androgens, so part of the assessment is excluding them. That's why testing often includes thyroid function and prolactin, and sometimes other hormones, to make sure the symptoms aren't being driven by something else. This is best done with a clinician who can interpret the whole set of results together.

Why a diagnosis matters

Getting clarity isn't just about a label. PCOS is linked to longer-term risks such as type 2 diabetes, so knowing about it means those can be monitored. It also opens the door to managing symptoms — from periods and skin to fertility — and lifestyle steps that genuinely help.

When to get checked

If your periods are irregular or absent, or you have persistent acne or unwanted hair growth, it's worth investigating rather than living with the uncertainty. A hormone panel and a conversation with a clinician are a sensible first step.

Written by Dr Ibrar Ahmed — MBChB MRCP MRCGP PhD PG Dip (Cardiology)
Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic