Step-by-step flowchart: Amenorrhea workup

Amenorrhea questions on USMLE are rarely about memorizing a giant differential—they’re about running a clean, fast algorithm. If you can move step-by-step (and know what each branch means physiologically), you’ll crush both vignette-style questions and real-life clinic logic.

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Define the problem (so you don’t get tricked)

Amenorrhea = absence of menses.

Primary amenorrhea (Step 1 + Step 2 classic)

• No menses by age 15 with normal growth/secondary sex characteristics
  OR
• No menses by age 13 with no secondary sex characteristics
  OR
• No menses within 3 years of thelarche

Secondary amenorrhea

• Previously menstruating, now absent:
  • $\ge 3$ months if previously regular
  • $\ge 6$ months if previously irregular

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The one-liner you should hear in your head

“Amenorrhea is pregnancy until proven otherwise—then prolactin/TSH—then estrogen status—then figure out if it’s the ovaries, brain, or outflow tract.”

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Visual mnemonic device: the “Amenorrhea Ladder”

Climb from most common → most high-yield:

1. Pregnancy
2. Prolactin (and meds/pituitary)
3. Thyroid
4. Estrogen status (withdrawal bleed?)
5. FSH/LH pattern (ovary vs hypothalamus/pituitary)
6. Outflow tract (Asherman, Müllerian issues)

Mnemonic: PPT-EFO (“Pee Pee Then Evaluate FSH to find Outflow”)
It’s goofy—but it keeps you moving.

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Step-by-step flowchart: secondary amenorrhea workup (the USMLE core)

Step 0: Always start here

1) Rule out pregnancy

• Order: urine $\beta$-hCG (or serum if needed)
• Why it matters: most common cause of secondary amenorrhea

If pregnant → manage pregnancy-related issue.
If not pregnant → continue.

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Step 1: Screen for endocrine “usual suspects”

2) Check TSH and prolactin

• TSH: hypothyroidism can raise TRH → ↑ prolactin → ↓ GnRH
• Prolactin: high prolactin suppresses GnRH → ↓ FSH/LH → anovulation/amenorrhea

If prolactin is high:

• Review meds (high-yield): antipsychotics (risperidone), metoclopramide, opioids
• Consider pituitary adenoma:
  • MRI brain if markedly elevated prolactin, symptoms (headache, bitemporal hemianopsia), or persistent elevation off meds
• Treat: dopamine agonist (cabergoline > bromocriptine), surgery if indicated

If TSH abnormal: treat thyroid disease.

If TSH and prolactin are normal → continue.

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Step 2: The key fork—Is there estrogen?

3) Progestin challenge test

• Give progestin (e.g., medroxyprogesterone) → stop → see if withdrawal bleeding occurs

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Step 3A: If bleed is positive → think anovulation

4) Evaluate for PCOS and chronic anovulation

High-yield features of PCOS:

• Irregular menses, infertility
• Hyperandrogenism (hirsutism, acne)
• ± polycystic ovaries on ultrasound

High-yield labs (pattern recognition):

• Often ↑ LH:FSH ratio (not required for diagnosis)
• Androgens may be elevated
• Exclude other causes if severe virilization: androgen-secreting tumor, late-onset CAH

USMLE management pearl:
Chronic anovulation → unopposed estrogen → endometrial hyperplasia/cancer risk.
Protect the endometrium with cyclic progestin or combined OCPs.

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Step 3B: If no bleed → decide “low estrogen” vs “blocked exit”

5) Estrogen–progestin challenge

• Give estrogen then progestin → see if bleeding occurs

Outflow tract high-yields:

• Asherman syndrome (intrauterine adhesions after D&C, endometritis)
  • Classic: secondary amenorrhea + infertility ± cyclic pelvic pain
  • Dx: hysteroscopy (or HSG)
• Cervical stenosis (post-procedural)

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Step 4: If hypoestrogenism → localize with FSH/LH

6) Check FSH (± LH, estradiol)

This step tells you if the problem is ovary vs brain.

Functional hypothalamic amenorrhea (FHA) clue set:

• Low BMI, endurance athlete, eating disorder, major stress
• Low GnRH → low FSH/LH → low estradiol
• Consequence: low bone density (think stress fractures)

Primary ovarian insufficiency (POI) clue set:

• <40 years, hot flashes, vaginal dryness
• High FSH, low estradiol
• Etiologies to remember: Turner (45,X), FMR1 premutation, autoimmune, iatrogenic

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Quick branch for PRIMARY amenorrhea (high-yield mini-flow)

Primary amenorrhea is where USMLE loves anatomy + genetics.

Step 1: Are secondary sex characteristics present?

• Yes → estrogen is present → think outflow tract or anatomic absence
• No → low estrogen → think gonadal failure or hypothalamic/pituitary

Step 2: Is a uterus present? (pelvic US is your friend)

If no uterus

Think: Androgen insensitivity vs Müllerian agenesis
Use testosterone level + karyotype:

If uterus is present

• If no secondary sex characteristics: evaluate FSH
  • High FSH: gonadal dysgenesis (e.g., Turner)
  • Low FSH: hypothalamic/pituitary cause (GnRH deficiency, FHA)

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“If you only memorize 6 things” (rapid USMLE hits)

• 1) Pregnancy test first, always.
• 2) Prolactin + TSH are the next fastest, highest-yield labs.
• 3) Progestin challenge:
  • Bleed = estrogen present → anovulation (PCOS)
  • No bleed = low estrogen or outflow problem
• 4) Estrogen–progestin challenge separates low estrogen from outflow obstruction.
• 5) FSH high = ovary failure (POI); FSH low/normal = hypothalamus/pituitary.
• 6) Primary amenorrhea: check uterus presence to split MRKH vs CAIS.

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Micro-table: common vignette triggers → diagnosis