Pregnancy Test First, Then Comprehensive Workup
When a woman presents with 6 months of amenorrhea, immediately perform a β-human chorionic gonadotropin (β-hCG) pregnancy test as the essential first step, followed by a systematic hormonal panel including FSH, LH, prolactin, TSH, free T4, estradiol, and AMH to identify the underlying cause 1.
Why Pregnancy Testing Comes First
Even with 6 months of amenorrhea, pregnancy must be definitively excluded before pursuing other diagnoses. The Endocrine Society guidelines explicitly state that pregnancy exclusion is the mandatory starting point for any amenorrhea workup 1. While 6 months makes pregnancy seem unlikely, ectopic pregnancy, retained products of conception, or gestational trophoblastic disease can present with prolonged amenorrhea and positive β-hCG.
The Complete Initial Laboratory Panel
After ruling out pregnancy, obtain the following tests simultaneously 1:
- Serum FSH and LH - Distinguishes hypothalamic/pituitary dysfunction (low/normal) from primary ovarian insufficiency (elevated)
- Estradiol (E2) - Assesses estrogen status and ovarian function
- Prolactin - Screens for hyperprolactinemia (common cause of amenorrhea)
- TSH and free T4 - Identifies thyroid dysfunction
- AMH (anti-Müllerian hormone) - Evaluates ovarian reserve
- Total testosterone and DHEA-S - If clinical signs of hyperandrogenism present
- 8 AM 17-hydroxyprogesterone - If suspecting late-onset congenital adrenal hyperplasia
Additional Essential Testing
The guidelines recommend obtaining 1:
- Complete blood count
- Comprehensive metabolic panel (electrolytes, glucose, BUN, creatinine, liver function)
- ESR/CRP if chronic illness suspected
Physical Examination Priorities
Look specifically for these findings 1:
- Weight and BMI trends - Energy deficit is a primary cause of functional hypothalamic amenorrhea
- Vital signs - Bradycardia suggests energy restriction
- Skin findings - Hypercarotenemia, acanthosis nigricans (insulin resistance), hirsutism, acne
- Galactorrhea - Indicates hyperprolactinemia
- Visual field testing - Screens for pituitary mass
- External gynecologic exam - Assesses estrogen status (thin, reddened mucosa indicates deficiency)
Critical History Elements
Ask specifically about 1:
- Energy availability - Exercise patterns, dietary intake, recent weight changes
- Psychosocial stress - Multiple minor stressors can be more disruptive than one major stressor
- Eating behaviors - Binging, purging, restrictive patterns
- Medications - Antipsychotics, antidepressants, contraceptives, opioids all affect menses
- Family history - Eating disorders, early menopause, endocrine conditions
Common Pitfall to Avoid
Do not assume 6 months of amenorrhea rules out pregnancy. While 2 shows that pregnancy tests have 90% sensitivity on the first day of missed menses and 97% by one week later, unusual presentations (ectopic pregnancy, molar pregnancy) can occur with prolonged amenorrhea. The β-hCG test takes minutes and prevents catastrophic misdiagnosis.
Interpreting the Pattern
The hormone pattern matters more than absolute values 1:
- Low/normal FSH + low estradiol = Functional hypothalamic amenorrhea or pituitary disorder
- Elevated FSH (>40 IU/L) + low estradiol = Primary ovarian insufficiency
- Elevated prolactin = Hyperprolactinemia (obtain MRI if >100 ng/mL or any neurologic symptoms)
- Elevated androgens = PCOS or other hyperandrogenic disorder
Why This Systematic Approach Matters
Six months of amenorrhea represents significant reproductive dysfunction with implications for bone density, cardiovascular health, and fertility 3, 4. The systematic laboratory approach identifies treatable causes (thyroid disease, hyperprolactinemia) versus conditions requiring long-term management (primary ovarian insufficiency, functional hypothalamic amenorrhea). The pattern of results guides whether the patient needs brain imaging, karyotyping, or immediate intervention for energy deficit 1.