How is PCOS Diagnosed?
Understanding the Tests, Examinations and Criteria Used to Diagnose Polycystic Ovary Syndrome
Introduction
If you think you might have Polycystic Ovary Syndrome (PCOS), or you've recently been told that you do, you may be wondering how doctors reach that diagnosis.
Unlike some medical conditions, there isn't a single blood test, scan or examination that can definitively confirm PCOS. Instead, healthcare professionals look at a combination of your symptoms, medical history, hormone levels and, in some cases, an ultrasound scan of your ovaries.
This can sometimes make the diagnostic process feel confusing. You may have symptoms of PCOS but a normal ultrasound, or you may have polycystic-looking ovaries but not have PCOS at all. Some women are diagnosed quickly, while others spend years searching for answers because their symptoms don't fit the "typical" picture.
The good news is that doctors now use internationally recognised diagnostic criteria to help ensure women receive an accurate diagnosis while ruling out other conditions that can cause similar symptoms.
In this article, we'll explain how PCOS is diagnosed, why certain tests are performed and what your results may mean.
Quick Summary
There is no single test that diagnoses PCOS.
Doctors diagnose PCOS using a combination of symptoms, medical history, blood tests and sometimes an ultrasound scan.
Most healthcare professionals use the Rotterdam Criteria, which require two out of three specific features to be present.
Other medical conditions must first be excluded because they can cause similar symptoms.
Diagnosis can be more challenging during adolescence because irregular periods are common in the first few years after puberty.
Why Isn't There a Single Test?
Many medical conditions can be diagnosed with one specific test.
A pregnancy test measures the hormone hCG.
Diabetes can often be diagnosed using blood glucose or HbA1c levels.
PCOS is different.
That's because it isn't caused by one abnormal hormone or one physical change. Instead, it is a syndrome—a collection of signs and symptoms that tend to occur together.
Every woman with PCOS has her own unique combination of symptoms. One may have irregular periods and acne, while another has excess hair growth and difficulty conceiving. A third may have very few symptoms apart from irregular ovulation.
Because of this variation, doctors must look at the whole picture rather than relying on a single investigation.
The Rotterdam Criteria
Today, most healthcare professionals use the Rotterdam Criteria, which were first introduced in 2003 and are recommended by international guidelines.
According to these criteria, a diagnosis of PCOS can usually be made if two out of the following three features are present, after other possible causes have been excluded.
1. Irregular or Absent Ovulation
This usually shows itself as irregular menstrual periods.
Your periods may:
Occur less frequently than every 35 days.
Be completely absent for several months.
Be unpredictable in timing.
Stop altogether.
Some women still bleed regularly but do not actually release an egg each month. This is known as anovulation and may only become apparent when trying to conceive.
2. Evidence of Higher Androgen Levels
Androgens are hormones that are often thought of as "male hormones", but women naturally produce them too.
In PCOS, androgen levels may be higher than expected.
Doctors look for evidence in two ways.
Clinical signs
These include:
Excess facial hair.
Hair growth on the chest, abdomen or back.
Persistent acne.
Oily skin.
Thinning hair on the scalp.
Blood tests
Sometimes androgen levels are measured directly.
These may include:
Total testosterone.
Free testosterone.
Free androgen index.
DHEAS (dehydroepiandrosterone sulphate).
Not every woman with PCOS has abnormal blood results, which is why symptoms remain just as important.
3. Polycystic Ovaries on Ultrasound
An ultrasound scan may show multiple small follicles around the edge of the ovary.
These are often described as looking like a "string of pearls."
Despite the name, these are not ovarian cysts.
They are immature follicles that began developing but did not reach ovulation.
Modern ultrasound machines are much more sensitive than those used when the Rotterdam Criteria were first introduced. As a result, the number of follicles considered "polycystic" has changed over time, and specialists interpret scans using updated guidance.
Importantly, an ultrasound alone cannot diagnose PCOS.
Many healthy women—particularly younger women—have polycystic-appearing ovaries without having the syndrome.
Why Other Conditions Must Be Excluded
One of the most important parts of diagnosing PCOS is making sure something else isn't causing the symptoms.
Several conditions can produce irregular periods, acne or excess hair growth.
Before confirming PCOS, your doctor may investigate other possible causes, including:
Thyroid disorders.
High prolactin levels.
Congenital adrenal hyperplasia.
Cushing's syndrome.
Androgen-producing tumours (rare).
Premature ovarian insufficiency.
Hypothalamic amenorrhoea, often linked to significant weight loss, excessive exercise or chronic stress.
Although these conditions are much less common than PCOS, identifying them is important because they require different treatment.
What Questions Will Your Doctor Ask?
Your medical history provides valuable clues.
You may be asked about:
When your periods started.
How regular your menstrual cycle is.
Whether you've noticed changes in facial or body hair.
Acne or oily skin.
Hair thinning.
Weight changes.
Difficulty becoming pregnant.
Family history of PCOS or diabetes.
Current medications.
Exercise and eating habits.
Although some questions may seem unrelated, they help your healthcare professional build a complete picture of your health.
Blood Tests Used When Investigating PCOS
Blood tests are usually performed for two reasons.
Firstly, they help identify hormonal patterns that support a diagnosis of PCOS.
Secondly, they help rule out other conditions.
Depending on your symptoms, your doctor may request tests such as:
Hormone Tests
Testosterone.
SHBG (Sex Hormone Binding Globulin).
Free androgen index.
LH.
FSH.
Oestradiol.
Prolactin.
Thyroid function tests.
17-hydroxyprogesterone (when appropriate).
Metabolic Tests
Because PCOS increases the risk of insulin resistance and type 2 diabetes, additional tests may include:
HbA1c.
Fasting glucose.
Lipid profile.
Liver function tests.
Some women may also undergo an oral glucose tolerance test, particularly if they have additional risk factors.
Is an Ultrasound Always Needed?
Not necessarily.
In adult women, an ultrasound can be helpful if the diagnosis remains uncertain.
However, current international guidelines advise that ultrasound is not routinely recommended for diagnosing PCOS in adolescents, because ovaries naturally contain many follicles during the years following puberty. Using ultrasound too early can lead to over-diagnosis.
Instead, diagnosis in teenagers focuses more on persistent menstrual irregularities and evidence of androgen excess over time.
Can You Have PCOS Without Polycystic Ovaries?
Yes.
This surprises many women.
Remember, under the Rotterdam Criteria, only two out of three features are required.
For example, you may have:
Irregular ovulation.
High androgen levels.
Even if your ultrasound appears normal, you may still meet the criteria for PCOS.
Equally, you may have polycystic-appearing ovaries but regular ovulation and no signs of androgen excess. In that case, you would not usually be diagnosed with PCOS.
Why Diagnosis Can Take So Long
Many women describe years of frustration before receiving a diagnosis.
There are several reasons for this.
Symptoms often develop gradually.
Different women experience different combinations of symptoms.
Irregular periods may initially be dismissed as "just one of those things."
Acne may be treated by a dermatologist.
Difficulty conceiving may not become apparent until years later.
Healthcare professionals may see each symptom separately rather than recognising the underlying pattern.
Fortunately, awareness of PCOS has improved significantly over recent decades, and many women are now diagnosed earlier than in the past.
What Happens After Diagnosis?
Receiving a diagnosis of PCOS is often the beginning rather than the end of the journey.
Your healthcare professional will discuss which aspects of the condition are affecting you most.
For some women, the priority is regulating menstrual cycles.
For others, it may be managing acne or unwanted hair growth.
Some women seek treatment because they wish to become pregnant, while others are more concerned about long-term health risks such as diabetes or cardiovascular disease.
Treatment is therefore highly individual and should be tailored to your symptoms, your overall health and your personal goals.
Key Takeaways
PCOS is diagnosed using a combination of symptoms, blood tests and sometimes ultrasound findings.
Most doctors use the Rotterdam Criteria, requiring two out of three key features for diagnosis.
There is no single blood test or scan that can diagnose PCOS.
Other medical conditions must be excluded before confirming the diagnosis.
Not every woman with PCOS has polycystic ovaries, and not every woman with polycystic ovaries has PCOS.
An accurate diagnosis helps guide appropriate treatment and long-term health monitoring.
Frequently Asked Questions
Can I have PCOS if my periods are regular?
Yes. Some women ovulate irregularly despite having apparently regular cycles, while others meet the diagnostic criteria because of androgen excess and polycystic ovaries. Further assessment may be needed.
Can a normal blood test rule out PCOS?
No. Hormone levels can fluctuate, and not every woman with PCOS has abnormal blood results. Diagnosis is based on the overall clinical picture rather than one test.
Does everyone with PCOS need an ultrasound?
No. Depending on your age and symptoms, your doctor may be able to make the diagnosis without an ultrasound. In adolescents, ultrasound is generally not recommended for diagnosis because normal ovaries can appear polycystic during puberty.
Can PCOS be diagnosed after menopause?
It becomes more challenging because menstrual cycles have stopped and ovarian appearance changes with age. Doctors usually rely on a woman's previous history of symptoms and reproductive health when considering whether she had PCOS before menopause.
References
This article should reference high-quality, evidence-based sources, including:
International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome
European Society of Human Reproduction and Embryology (ESHRE)
American Society for Reproductive Medicine (ASRM)
National Institute for Health and Care Excellence (NICE)
Peer-reviewed research on the Rotterdam Criteria and PCOS diagnosis