Reasoning GP · Algorithm · 1-page summary
Amenorrhoea — primary and secondary
For: adolescents and adults with a uterus and absent periods. Not for: confirmed pregnancy (antenatal care; EPU if pain or bleeding). Primary amenorrhoea and structural causes → specialist (block 1).
Core rule: exclude pregnancy first in anyone with a uterus where pregnancy is possible, regardless of contraception — it is the commonest cause of secondary amenorrhoea. Then classify primary vs secondary and localise the level with FSH/LH, prolactin and TSH.
0Stop — call 999 now — before any history
- Possible ectopic: lower abdominal pain, shoulder-tip pain and haemodynamic instability → 999. Positive βhCG with pain, bleeding or syncope → Same-day EPU / ED, immediately
- Pituitary apoplexy: sudden severe headache with visual field defect or visual loss → 999
- Adrenal crisis: collapse, hypotension, vomiting, pigmentation, preceding weight loss → 999
- Severe malnutrition with arrhythmia or collapse → 999. Hypokalaemia from purging can cause fatal arrhythmias.
1Triage by type — after a pregnancy test
| Finding | Action |
|---|---|
| All | Urine βhCG today; serum βhCG if negative but suspicion high, or pain/bleeding. |
| Primary (early) | No breast development by 13, abnormal genitalia, cyclic pelvic pain, virilisation or Turner features → Urgent paediatric/adolescent gynae or endocrine |
| Primary | No menarche by 15, or >3 years after breast development → gynaecology promptly; do not wait until 16. |
| Secondary | Regular periods absent ≥3 months, or irregular absent ≥6 months → work up in primary care. |
2Screen — one row is enough
- Pituitary mass: galactorrhoea, headache, bitemporal field loss → Same-day endocrine / A&E.
- Androgen-secreting tumour: rapid virilisation, clitoromegaly, deepening voice, markedly raised testosterone (vs local assay range) → Urgent gynae / endocrine
- Eating disorder: BMI <17.5 or rapid weight loss with lanugo, bradycardia or electrolyte disturbance → Same-day assessment (MEED).
- Outflow: post-curettage cyclical pain, no bleeding → gynaecology; haematometra or acute obstruction → Same-day
- POI: age <40, menopausal symptoms, raised FSH on two samples 4–6 weeks apart → HRT/CHC, bone and fertility plan (blocks 5–6).
3Assess — once blocks 0–2 are answered
☐ BMI, lanugo ☐ thyroid ☐ hirsutism, clitoromegaly ☐ galactorrhoea ☐ visual fields ☐ Turner stigmata ☐ striae, pigmentation, acanthosis ☐ drugs raising prolactin (antipsychotics, opioids, metoclopramide, domperidone, methyldopa, verapamil)
☐ Bloods: FSH + LH (day 2–5 if cycling), prolactin (rested), TSH ± free T4; oestradiol if hypogonadism suspected; testosterone + SHBG if hyperandrogenism; HbA1c by risk.
Chaperone intimate examination; primary amenorrhoea → consider USS instead. Not routine: progesterone challenge, inhibin B, ACTH, AMH.
4Classify — only if the screen is negative
- Hypothalamic — low/normal FSH, low oestradiol; low weight, exercise (RED-S), stress; anosmia → Kallmann.
- PCOS — 2 of 3: ovulatory dysfunction, hyperandrogenism, polycystic ovaries, after excluding pregnancy, thyroid, prolactin, non-classic CAH (17-OHP) and tumour. No USS needed if the first two present.
- POI — <40 years, high FSH on two samples 4–6 weeks apart, low oestradiol. Never on a single FSH or AMH.
- Raised prolactin — repeat rested sample; review pregnancy, drugs, hypothyroidism, renal disease, macroprolactin. Persistent unexplained → endocrinology ± MRI.
- Structural / systemic — imperforate hymen, MRKH, Asherman's, Turner → specialist; thyroid, Cushing's, chronic illness.
- Uncertain — say so. Review at 3 months; no periods after 6 months of appropriate treatment → repeat tests, reconsider diagnosis.
5Treat today — by cause; doses: NICE/SPC, BNF, local formulary
- Confirmed POI: offer HRT or CHC unless contraindicated, until at least ~50–51; progestogen if uterus present. HRT is not contraceptive; no CHC with HRT without specialist advice. Calcium 700–1000 mg/day diet + vitamin D 800–2,000 IU/day.
- PCOS: lifestyle (5–10% weight loss if overweight); endometrial protection with CHC (if UKMEC-suitable) or cyclical progestogen. Metformin for metabolic risk (500 mg once daily with food, titrate).
- Functional hypothalamic: restore energy balance (dietetic, eating-disorder, sports, psychological input) — not hormones first.
- Drug-induced prolactin: stop/switch with the prescribing team; no dopamine agonist without a specialist. Hypothyroid: levothyroxine.
6Refer routinely
- Confirmed POI → specialist menopause/reproductive medicine (uncertainty, fertility, comorbidity, genetic/autoimmune); prompt fertility counselling.
- Wants pregnancy → reproductive medicine; do not wait 12 months with anovulation, POI or endocrine disorder.
- Eating disorder → CAMHS (<18) or adult ED team; RED-S → sports medicine + dietitian. Uncomplicated PCOS: primary care.
7Never reassure by
- Reported contraception or "can't conceive" — test βhCG.
- Labelling rapid virilisation or markedly raised androgens as PCOS.
- A single FSH, or AMH, to diagnose POI.
- "No periods" — ovulation can return before menses.
- A normal BMI — BMI alone does not exclude an eating disorder.
- Imaging raised prolactin before a drug review and rested repeat.
8Safety-net — say it, then document it
999 “Call 999 for sudden severe headache with loss of vision, collapse, or severe tummy or shoulder pain with a positive pregnancy test.” Same day: “Milky nipple discharge, vision change, fast-growing hair, deeper voice, severe pelvic pain, or pain with a positive test — call us today.”
Follow-up: 4–6 weeks (results, tolerability); 3 months if no periods. Reliable contraception from the start of treatment.
✓Safe to leave primary care only if — all five, documented
Pregnancy excluded; no block 0–2 row applies
Primary vs secondary recorded; visual fields and BMI done
FSH/LH, prolactin, TSH explain the level, or uncertainty stated
Bone, contraception and fertility addressed; review date set
Safety-net given and documented
Summary of the full Reasoning GP amenorrhoea algorithm, which holds the detail, examination, investigations and evidence. Sources: NICE NG23, NG69; International PCOS guideline 2023; ESHRE POI 2024; Endocrine Society FHA 2017 and prolactinoma guidelines; Society for Endocrinology 2024; RCPsych MEED 2022; BSPED Turner. Clinical reference — follow local policies and check doses: NICE/SPC, BNF.