Irregular periods, acne, excess facial hair and difficulty conceiving can raise the possibility of polycystic ovary syndrome (PCOS). Hormone testing can help investigate those concerns, but there is no single PCOS blood test that definitively confirms the condition. Diagnosis depends on the whole picture: symptoms, menstrual history, relevant laboratory findings and sometimes an ultrasound.
This guide explains which hormones may be useful, how menstrual timing changes interpretation and why assessing metabolic health is often part of a sensible PCOS review.
What is PCOS?
PCOS is a common endocrine and metabolic condition associated with disrupted ovulation and increased androgen activity in some people. It may affect periods, skin, hair growth and fertility. Features differ: one person may have irregular periods and acne, while another mainly notices difficulty becoming pregnant.
The name can be misleading. You do not need visible ovarian 'cysts' on a scan to have PCOS, and finding polycystic-looking ovaries does not prove the syndrome is present.
In adults, commonly used diagnostic criteria consider at least two of three features after excluding other explanations: irregular or absent ovulation; clinical or biochemical evidence of androgen excess; and characteristic ovarian morphology on ultrasound. Specialist guidelines continue to evolve, and diagnosis in adolescents requires particular care.
Which hormones are tested for PCOS?
Total testosterone and calculated free androgen measures
Testosterone can be elevated in PCOS, particularly when symptoms suggest androgen excess. Because much circulating testosterone is bound to proteins, clinicians may also consider sex hormone-binding globulin (SHBG) and a calculated free androgen index. An abnormal number is not specific for PCOS, and a normal result does not automatically exclude it.
DHEA-S
Dehydroepiandrosterone sulphate (DHEA-S) is produced mainly by the adrenal glands. It can assist investigation of androgen excess and sometimes helps clinicians distinguish ovarian from adrenal contributions. Markedly abnormal values or rapidly progressing symptoms need further assessment.
LH and FSH
Luteinising hormone (LH) and follicle-stimulating hormone (FSH) are involved in the menstrual cycle. Their concentrations change across the cycle and can be affected by contraception. The LH-to-FSH ratio is sometimes discussed online, but it is not a reliable stand-alone diagnostic test for PCOS.
Oestradiol and progesterone
Oestradiol varies during the menstrual cycle. Progesterone can help assess whether ovulation has occurred when collected at an appropriate point, typically about seven days before an expected period rather than automatically on 'day 21' for everyone. Cycle irregularity makes choosing the sampling date harder; ask for individual guidance.
Prolactin and thyroid tests
Other conditions can resemble PCOS. Prolactin and thyroid function may be checked to investigate menstrual disturbance or exclude alternatives. A test panel that reports testosterone alone can miss important contextual information.
Why menstrual cycle timing matters
Hormone concentrations are dynamic. A result taken early in the cycle can differ from one taken just before menstruation. People using the combined oral contraceptive pill may have altered androgen measurements, making interpretation more challenging.
Do not stop contraception simply to get a laboratory result. If a clinician needs a medication-free assessment, they should explain the risks, alternatives and timing. The best approach depends on whether the primary concern is acne, irregular bleeding, fertility or a possible endocrine disorder.
Is an ultrasound necessary?
Not always. In adults with clear evidence of irregular ovulation and androgen excess, an ultrasound may not add enough to change diagnosis. Conversely, an ultrasound appearance alone is insufficient. Imaging may be valuable when the diagnosis is uncertain or other pelvic symptoms need investigation.
For younger patients, diagnostic criteria differ because menstrual irregularity and ovarian morphology may be part of normal development after the first period. A paediatric or adolescent specialist may be appropriate.
PCOS and metabolic health
PCOS is not only a reproductive hormone issue. Some people also have insulin resistance, dyslipidaemia and an increased risk of type 2 diabetes. Depending on the person's risk and clinical history, a clinician may recommend blood pressure measurement, an assessment of glucose regulation and a lipid profile.
HbA1c can provide useful information, although a clinician may select an oral glucose tolerance test in certain circumstances, particularly around fertility or pregnancy planning. Results should inform a personalised care plan rather than becoming a label that every person with PCOS will develop diabetes.
Signs that need prompt review
Seek medical advice for very heavy or prolonged abnormal bleeding, new severe pelvic pain or symptoms that develop rapidly. Rapid-onset facial hair growth, voice deepening or other pronounced signs of androgen excess are not typical of uncomplicated PCOS and require medical evaluation for other causes.
An absence of periods for a prolonged period also deserves review. Treatment may be needed to protect the womb lining even when pregnancy is not a goal.
PCOS blood testing in London
London Blood Tests offers a Hormonal Health Profile covering testosterone, SHBG, DHEA-S, LH, FSH, oestradiol, progesterone, prolactin and related markers. It can provide useful laboratory information for a clinician-led assessment. It is not a self-contained PCOS diagnosis, and the right tests depend on the reason for testing.
Private blood collection may be arranged at a London clinic or, where offered, through home phlebotomy. Mention your menstrual dates, contraception, pregnancy possibility and medicines when discussing which test to book.
Frequently asked questions
Can PCOS be diagnosed with a hormone blood test alone?
No. Hormones can contribute evidence, but diagnosis requires symptoms, history, exclusion of other causes and sometimes ultrasound.
Is high testosterone always PCOS?
No. Increased testosterone has other possible causes and must be interpreted clinically.
What day of my cycle should I test?
There is no single day suitable for every hormone. The clinician should advise based on which markers are required and your cycle pattern.
Does normal testosterone mean I cannot have PCOS?
No. Some people meet other diagnostic features without a clearly elevated testosterone result.
Should I check glucose and cholesterol as well?
Metabolic assessment may be appropriate because PCOS can be associated with insulin resistance and cardiovascular risk factors.
The key point
A well-chosen PCOS hormone test can answer important questions, but clinical interpretation matters more than collecting as many hormones as possible. Start with your symptoms and menstrual history, then choose the investigations that genuinely inform care.
Medical sources: Oxford University Hospitals – PCOS diagnostic criteria; NHS Sussex – PCOS referral pathway.
Medical information only. Consult a qualified clinician for diagnosis and treatment of menstrual or fertility concerns.