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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

PCOS diagnostic criteria and differentials

Obstetrics and gynaecology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

RapidFull
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Virilisation is not routine PCOS

Rapid androgenic change, marked biochemical androgen excess, postmenopausal onset or an abdominal mass may represent an ovarian or adrenal tumour and should not be delayed by a routine PCOS work-up.

Action: Repeat a reliable androgen profile promptly, examine for virilisation and masses, and obtain urgent endocrinology or gynaecology assessment with targeted ovarian and adrenal imaging.

Overview

Apply adult and adolescent PCOS criteria correctly, document hyperandrogenism and ovulatory dysfunction, and exclude pregnancy, endocrine mimics and dangerous androgen excess.

PCOS is a heterogeneous endocrine-metabolic syndrome expressed through ovulatory dysfunction and androgen excess. Its name can mislead: the ovarian structures are small follicles, and neither an ovarian cyst nor a scan appearance is required in every adult. In June 2026 the NHS adopted the public-facing term polyendocrine metabolic ovarian syndrome, abbreviated PMOS, while the current international professional guideline and the established diagnostic literature use PCOS. Acknowledge both terms so that a patient is not left thinking they have two separate disorders.

The 2023 international evidence-based guideline retains a modified Rotterdam framework for adults. After relevant alternatives are excluded, two of three domains establish the diagnosis: irregular cycles or other evidence of ovulatory dysfunction; clinical or biochemical hyperandrogenism; and polycystic ovarian morphology. In adults, an appropriately measured AMH may define the morphology domain instead of ultrasound, but it must not be used alone or added to ultrasound as a fourth route. If ovulatory dysfunction and hyperandrogenism are already present, morphology testing adds no diagnostic requirement.

Aetiology

01

Polygenic susceptibility

Multiple inherited variants interact with developmental and environmental influences, producing familial clustering without a single diagnostic gene in most people.

02

Insulin-androgen interaction

Insulin resistance and compensatory hyperinsulinaemia amplify ovarian androgen production and reduce hepatic SHBG, increasing biologically available androgen in many phenotypes.

03

Neuroendocrine dysregulation

Altered gonadotrophin pulsatility and ovarian feedback can favour theca-cell androgen output and disrupt selection of a dominant follicle.

Pathophysiology

  1. 1
    Androgen production increases

    Ovarian theca signalling, sometimes reinforced by insulin, increases androgen exposure and drives hirsutism, acne and altered follicular development.

  2. 2
    Follicle selection stalls

    Many small antral follicles accumulate when coordinated maturation and dominant-follicle selection fail, creating irregular ovulation rather than dangerous cyst formation.

  3. 3
    Binding proteins fall

    Hyperinsulinaemia can lower hepatic SHBG, so free testosterone rises even when total testosterone appears only modestly changed.

  4. 4
    Endometrium loses progesterone cycles

    Infrequent ovulation removes regular luteal progesterone exposure, allowing prolonged oestrogen-driven proliferation and unpredictable shedding in some patients.

Clinical features and red flags

Ovulatory dysfunction

Persistent cycles outside age-specific ranges, prolonged gaps or biochemical anovulation form one adult diagnostic domain after pregnancy and treatment effects are considered.

Clinical hyperandrogenism

Gradually progressive terminal hair in androgen-sensitive sites is the clearest clinical sign; acne and scalp hair loss are less specific when isolated.

Biochemical hyperandrogenism

Raised total or calculated free testosterone on a reliable assay supports the androgen domain, with DHEAS or androstenedione reserved for selected unresolved cases.

Adult ovarian morphology

A current threshold on technically adequate ultrasound, or a validated AMH assay used instead, can supply the third domain only in adults.

Adolescent risk state

An adolescent with only irregular cycles or hyperandrogenism should receive symptom care and planned reassessment rather than a premature ultrasound-driven lifelong label.

Red flags requiring action

  • Voice deepening, clitoromegaly, rapidly increasing muscle mass or fast progression of terminal hair suggests severe androgen excess rather than the usual gradual PCOS phenotype.
  • A very high or rapidly rising testosterone or DHEAS concentration requires confirmation with a high-quality assay and urgent investigation for ovarian or adrenal pathology.

Investigations

  1. 01
    Pregnancy test, TSH and prolactinFirst step
    Why
    Exclude common consequential alternatives to PCOS in a person with irregular or absent cycles.
    Interpretation and limitations
    A positive hCG changes the pathway; abnormal thyroid or persistent monomeric prolactin findings require cause-specific assessment and cannot be absorbed into a PCOS label.
  2. 02
    Total and calculated free testosterone
    Why
    Confirm biochemical hyperandrogenism when clinical assessment is absent, equivocal or requires quantification.
    Interpretation and limitations
    Use a high-quality total testosterone assay with SHBG for calculation; marked elevation or mismatch with a slow phenotype requires repeat confirmation and tumour assessment.
  3. 03
    Early-morning 17-hydroxyprogesterone
    Why
    Screen for non-classic 21-hydroxylase deficiency when androgen excess or ancestry makes it relevant.
    Interpretation and limitations
    An elevated screening value is not PCOS and needs endocrine interpretation, usually including a properly timed repeat or ACTH stimulation.
  4. 04
    Pelvic ultrasound
    Why
    Assess adult polycystic ovarian morphology and identify other pelvic pathology when morphology is diagnostically necessary.
    Interpretation and limitations
    Do not request it solely to confirm PCOS when irregular cycles and hyperandrogenism already coexist, and

Differential diagnosis

01

Functional hypothalamic amenorrhoea

Energy deficiency or stress suppresses gonadotrophins and oestradiol; multifollicular ovaries can coexist but do not convert central hypogonadism into PCOS.

02

Non-classic adrenal hyperplasia

Partial 21-hydroxylase deficiency causes androgen excess and irregular cycles, screened with appropriately timed 17-hydroxyprogesterone and confirmed endocrinologically.

03

Androgen-secreting tumour

Rapid virilisation, an abdominal mass or marked testosterone or DHEAS elevation suggests ovarian or adrenal neoplasia requiring urgent localisation.

04

Hyperprolactinaemia or thyroid disease

Either disorder can interrupt ovulation and coexist with weight or skin changes, but targeted hormone results identify a separate treatable mechanism.

05

Cushing syndrome

Proximal weakness, easy bruising, facial plethora and broad violaceous striae make pathological cortisol excess more plausible than nonspecific weight gain alone.

Management

01Adult criteriaDocument two diagnostic domainsFirst stepAn adult presents with irregular cycles, androgenic symptoms or a prior report of polycystic ovaries.+
  1. 1Define cycle pattern and assess clinical hyperandrogenism, pregnancy possibility, hormonal treatment, symptom tempo and red flags for severe endocrine disease.
  2. 2Confirm biochemical androgens when needed and exclude thyroid, prolactin, adrenal and other alternatives in proportion to the clinical presentation.
  3. 3Use ultrasound or AMH only if the morphology domain is needed, then record exactly which two of three domains establish the diagnosis.
02Adolescent assessmentAvoid premature morphology labelsIrregular menstruation or androgenic features arise during the years after menarche.+
  1. 1Interpret cycle length by time since menarche and distinguish physiological first-year irregularity from persistent abnormal patterns.

Complications

01

Metabolic disease

Insulin resistance raises the probability of dysglycaemia, type 2 diabetes and adverse cardiovascular risk factors across weight categories.

02

Endometrial pathology

Long untreated amenorrhoea, higher weight and diabetes compound the risk of endometrial hyperplasia and cancer from infrequent progesterone exposure.

03

Anovulatory infertility

Irregular dominant-follicle development reduces predictable ovulation, although spontaneous ovulation and conception remain possible and contraception may still be needed.

04

Psychological morbidity

Hirsutism, acne, body-image pressure, fertility uncertainty and weight stigma contribute to higher rates of depression, anxiety and disordered eating.

Monitoring and follow-up

  • Record the domains supporting diagnosis, assay method, hormonal treatment and excluded alternatives so future clinicians can audit rather than simply inherit the label.
  • Reassess adolescents with only one diagnostic feature at intervals determined by symptoms and no later than full reproductive maturity, around eight years after menarche.
  • Repeat androgen assessment promptly if clinical progression accelerates, virilisation appears or the biochemical result is markedly discordant with the original phenotype.
  • Review changing reproductive goals, bleeding pattern, mental health, eating behaviour, sleep and cardiometabolic risk even when the diagnostic criteria themselves remain met.
  • Do not serially repeat ultrasound or AMH to measure treatment response; neither tracks symptom control or long-term health adequately.

Special situations

Two domains can be enough

Established ovulatory dysfunction and hyperandrogenism diagnose adult PCOS after exclusions, so additional morphology testing can add cost without diagnostic value.

AMH replaces, not supplements

In adults an accepted AMH measure can substitute for ultrasound morphology, but using both double-counts the same ovarian domain.

Adolescence changes specificity

Irregular cycles, acne and multifollicular ovaries are common during normal maturation, which is why adolescent criteria require persistent dysfunction plus hyperandrogenism.

Contraception changes the laboratory

Combined pills increase SHBG and suppress androgen production, making normal results reassuring for treatment effect but poor evidence about the untreated phenotype.

Terminology is evolving

The NHS public term PMOS emphasises systemic endocrine-metabolic effects, while PCOS remains the term used in the current international diagnostic guideline and curriculum.

Common pitfalls

  1. 01

    Diagnosing PCOS from an ultrasound report alone or describing follicles as ovarian cysts that need removal.

  2. 02

    Using adult morphology or AMH criteria in an adolescent whose reproductive axis is still maturing.

  3. 03

    Ordering both AMH and ultrasound and counting them as separate diagnostic domains.

  4. 04

    Calling rapid virilisation or marked androgen elevation severe PCOS without urgent tumour-focused assessment.

  5. 05

    Interpreting a normal androgen panel obtained during combined oral contraception as proof that pretreatment hyperandrogenism never existed.

  6. 06

    Screening indiscriminately for rare endocrine syndromes while overlooking pregnancy, thyroid disease, prolactin and non-classic adrenal hyperplasia.

Practice

Two practice questions

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Question 1 of 2
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Obstetrics and gynaecologyOriginal SBA

Adult criteria without imaging

A 27-year-old has persistent cycles of 45 to 70 days and clinically significant hirsutism. Pregnancy, thyroid disease, hyperprolactinaemia and non-classic adrenal hyperplasia have been excluded. What best completes diagnostic assessment?

Choose one answer, then submit
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Sources and review status5 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Apply principles in context and verify current guidance when a decision affects care. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • RCOG international PCOS guideline
  • International PCOS recommendations 2023
  • NICE CKS polycystic ovary syndrome
  • NHS polyendocrine metabolic ovarian syndrome
  • RCOG PCOS long-term health information

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom

Cycle interpretation is age dependent. The first post-menarcheal year often reflects normal maturation. From one to less than three years after menarche, cycles shorter than 21 days or longer than 45 days are irregular; from three years after menarche, cycles shorter than 21 days, longer than 35 days or fewer than eight per year are irregular. Any cycle exceeding 90 days more than one year after menarche, primary amenorrhoea by age 15 or more than three years after breast development also requires assessment. Adolescents should not be diagnosed from adult ultrasound or AMH thresholds. They need both persistent ovulatory dysfunction and hyperandrogenism, and a person with only one domain can be described as at increased risk and reviewed by or before eight years after menarche.

Clinical hyperandrogenism includes hirsutism and, less specifically, severe acne or female-pattern hair loss. Use a standardised hirsutism score sensitively across different ethnic backgrounds and recognise that self-removal may hide hair growth. Biochemical testing is most useful when clinical signs are absent or uncertain. Measure total and calculated free testosterone or free androgen index using accurate assays; direct free-testosterone immunoassays perform poorly. Combined oral contraception raises SHBG and suppresses ovarian androgen production, so a result on treatment may be uninterpretable.

PCOS remains a diagnosis of inclusion plus exclusion. Test pregnancy whenever possible. Assess TSH and prolactin in cycle disturbance and measure early-morning follicular 17-hydroxyprogesterone when non-classic congenital adrenal hyperplasia is relevant. Cushing syndrome, acromegaly, severe insulin-resistance syndromes and androgen-secreting ovarian or adrenal disease are not screened indiscriminately; pursue them when phenotype, tempo or androgen magnitude supports the possibility. Functional hypothalamic amenorrhoea can coexist with polycystic morphology and is suggested by low energy availability and low oestradiol rather than androgen excess.

Ultrasound technique and threshold matter. In adults with adequate transvaginal imaging, follicle number per ovary is the preferred marker, interpreted using current equipment-specific thresholds; ovarian volume or follicles per section can be used when image quality is limited. Record cycle stage, dominant follicles, cysts and hormonal treatment. Transabdominal scanning is less sensitive and may rely more on ovarian volume. Never report a generic 'polycystic appearance' without considering age, route and diagnostic context.

At diagnosis, explain uncertainty honestly and document which two domains are met, which alternatives were assessed and whether hormones affected testing. The label carries implications for metabolic, endometrial, reproductive and psychological health, but phenotype varies and can change. Ask about eating disorders, body image, depression, anxiety, sleep and pregnancy plans without assuming weight or infertility. Revisit the diagnosis if features become rapidly progressive or the original evidence was only an ultrasound report.

Key points

  • In adults, diagnose PCOS after excluding relevant alternatives when at least two of three features are present: ovulatory dysfunction, clinical or biochemical hyperandrogenism, and polycystic ovarian morphology on ultrasound or an accepted adult AMH alternative.
  • When irregular cycles and hyperandrogenism are both established, ovarian ultrasound or AMH is unnecessary for diagnosis and can create confusion rather than certainty.
  • Do not use AMH as a standalone test, combine AMH and ultrasound to inflate the morphology criterion, or apply either test for diagnosis during adolescence.
  • Adolescents require both persistent ovulatory dysfunction defined by years since menarche and clinical or biochemical hyperandrogenism after mimics are excluded; review those with partial features over time.
  • Prefer calculated free testosterone or free androgen index with a reliable total testosterone assay; combined oral contraception makes biochemical interpretation difficult and may need a supervised three-month washout if testing is essential.
  • Exclude pregnancy, thyroid disease, hyperprolactinaemia and non-classic congenital adrenal hyperplasia in the appropriate presentation; investigate Cushing syndrome or androgen-secreting disease when their clinical signals are present.
  • Polycystic ovaries are follicles, not pathological cysts requiring drainage or removal, and morphology alone is common in people without the syndrome.
  • The NHS now uses the public-facing term polyendocrine metabolic ovarian syndrome, but current professional guidance and this curriculum retain PCOS; explain the terminology without changing the diagnostic construct.
Headache, visual change or galactorrhoea directs assessment toward pituitary disease and hyperprolactinaemia rather than assuming PCOS explains irregular cycles.
  • Cushingoid bruising, broad violaceous striae, proximal weakness or facial plethora warrants targeted cortisol assessment where clinical suspicion is genuine.
  • A positive pregnancy test, pelvic pain or abnormal bleeding must enter the pregnancy pathway before diagnostic hormone interpretation.
    • do not
    use morphology for adolescent diagnosis.
  • 05
    Anti-Müllerian hormone
    Why
    Provide an adult alternative to ultrasound for the ovarian-morphology domain when an assay-specific threshold is appropriate.
    Interpretation and limitations
    AMH is not a standalone PCOS test, should not be combined with ultrasound to double-count morphology and is unsuitable for adolescent diagnosis.
  • 06
    Targeted adrenal or cortisol assessment
    Why
    Investigate severe androgen excess, virilisation or convincing features of another endocrine syndrome.
    Interpretation and limitations
    The test and imaging sequence follows the suspected disorder; routine broad screening in a typical stable PCOS phenotype increases false positives.
    • 2
    Require hyperandrogenism as well as ovulatory dysfunction after excluding mimics; do not use ovarian ultrasound or AMH to make the diagnosis.
  • 3Treat distressing symptoms, discuss the uncertainty and schedule reassessment for a partial phenotype by full reproductive maturity.
    • 03Atypical phenotypeEscalate severe or rapid androgen excessEscalationVirilisation, rapid progression, a mass or androgen concentrations are disproportionate to usual PCOS.+
    1. 1Repeat total testosterone using a high-quality method and measure DHEAS with other tests selected from the clinical pattern.
    2. 2Arrange urgent ovarian and adrenal evaluation through endocrinology and gynaecology rather than waiting for routine lifestyle follow-up.
    3. 3Investigate Cushing syndrome, severe insulin resistance or other rare disease only through a focused pathway supported by clinical findings.
    04Diagnostic reviewRevisit an inherited labelA previous PCOS diagnosis rests on ultrasound alone, remote testing or evidence obtained during hormonal therapy.+
    1. 1Retrieve the original cycle, androgen and imaging evidence and ask whether two valid domains were ever demonstrated after exclusions.
    2. 2AlternativeIf biochemical testing is essential, plan any hormonal washout with alternative contraception and symptom support rather than stopping treatment casually.
    3. 3Retain, revise or remove the label transparently while continuing appropriate care for current symptoms and metabolic or endometrial risk.