What is the appropriate initial workup for a 16‑year‑old post‑pubertal female with primary amenorrhea?

Initial Workup for Primary Amenorrhea in a 16-Year-Old Female

For a 16-year-old with primary amenorrhea who has developed secondary sexual characteristics, begin with a pregnancy test, then measure FSH, LH, prolactin, TSH, and estradiol levels, and obtain a pelvic ultrasound to assess uterine and ovarian anatomy. 1, 2, 3

Immediate Assessment Required

This 16-year-old meets criteria for urgent evaluation since primary amenorrhea is defined as absence of menarche by age 16 years in the presence of other pubertal development, or by age 15 years regardless of pubertal status. 2, 3 The American College of Obstetricians and Gynecologists recommends immediate evaluation and potential referral to pediatric endocrinology or gynecology for girls meeting these criteria. 3

Initial Clinical Evaluation

History Components

• Pubertal development timeline: Document age of thelarche (breast development), presence and timing of pubic/axillary hair development, and any progression or arrest of pubertal changes. 2, 3
• Growth patterns: Assess height velocity and compare to parental heights to identify potential Turner syndrome or other chromosomal abnormalities. 2
• Weight and nutrition: Document current BMI, recent weight changes, eating patterns, and exercise habits to screen for functional hypothalamic amenorrhea or Female Athlete Triad. 1, 2
• Family history: Ask specifically about delayed puberty in relatives, as this may indicate constitutional delay or genetic conditions. 3
• Symptoms suggesting specific etiologies: Evaluate for galactorrhea (hyperprolactinemia), headaches or visual changes (pituitary pathology), hirsutism or acne (PCOS or hyperandrogenism). 1, 2

Physical Examination

• Tanner staging: Determine breast and pubic hair development stage—if no breast development by age 13, this represents delayed puberty requiring earlier intervention. 2, 3
• Critical red flag: Absence of pubic and axillary hair despite breast development suggests complete androgen insensitivity syndrome and requires karyotype testing. 2
• BMI calculation: Essential as obesity associates with PCOS while low BMI suggests hypothalamic amenorrhea. 1
• Thyroid examination: Palpate for enlargement or nodules. 1

Mandatory Laboratory Testing

First-Line Hormonal Panel

• Pregnancy test: Must be performed first to exclude pregnancy, even in patients denying sexual activity. 1, 2, 4
• FSH and LH: Elevated FSH (>40 mIU/mL) indicates primary ovarian insufficiency and requires repeat testing 4 weeks later for confirmation (two elevated values required for diagnosis). 1, 2, 3 An LH/FSH ratio >2 suggests PCOS. 1, 3
• Prolactin: Elevated levels (>20 μg/L) suggest hyperprolactinemia from pituitary adenoma or medication effect. 1, 2
• TSH: Identifies thyroid dysfunction as a reversible cause of amenorrhea. 1, 2, 3
• Estradiol: Low levels (<30 pg/mL) confirm hypoestrogenism and help differentiate functional hypothalamic amenorrhea from other causes. 1, 2

Timing Considerations

Draw blood samples for FSH, LH, and estradiol at any time in amenorrheic patients (no need to wait for specific cycle day). 1

Imaging Studies

Pelvic Ultrasonography

• Mandatory for all cases: Assess uterine presence and anatomy to exclude Müllerian agenesis or outflow tract obstruction. 2, 3
• Ovarian evaluation: Identify polycystic ovarian morphology or absent/streak ovaries. 1, 3
• Endometrial thickness: Thin endometrium (<5 mm) suggests estrogen deficiency; thick endometrium (>8 mm) suggests chronic anovulation with unopposed estrogen. 1
• Transvaginal ultrasound is more sensitive than transabdominal for identifying structural abnormalities, though transabdominal may be more appropriate in virginal adolescents. 3

Brain MRI Indications

Order brain MRI if FSH/LH are low (suggesting hypothalamic/pituitary dysfunction) or if patient has neurological symptoms such as headaches or visual changes. 3

Interpretation Algorithm Based on FSH Results

Elevated FSH (>40 mIU/mL): Primary Ovarian Insufficiency

• Confirm diagnosis: Repeat FSH 4 weeks later—two elevated values required. 1, 2
• Karyotype testing: Mandatory to identify Turner syndrome or other chromosomal abnormalities. 2, 3
• Critical counseling point: These patients can maintain unpredictable ovarian function and should not be presumed infertile. 1, 4
• Immediate referral: To endocrinology and gynecology for sex steroid replacement therapy to prevent osteoporosis, cardiovascular disease, and urogenital atrophy. 2, 3

Low FSH/LH: Hypothalamic or Pituitary Dysfunction

• Check estradiol: Low estradiol confirms hypogonadotropic hypogonadism. 2, 3
• Screen for functional causes: Assess energy availability (>30 kcal/kg fat-free mass/day), exercise patterns (>10 hours/week intense training warrants evaluation), and eating disorders. 1, 2
• Brain MRI indicated: To exclude pituitary adenoma or other central pathology. 3

Normal FSH with LH/FSH Ratio >2: Polycystic Ovary Syndrome

• Add androgen testing: Measure testosterone and androstenedione if clinical signs of hyperandrogenism present. 1
• Ultrasound findings: Look for polycystic ovarian morphology. 1, 2

Critical Red Flags Requiring Urgent Specialist Referral

• No breast development by age 13 years: Represents delayed puberty requiring endocrinology evaluation. 2, 3
• Breast development present but absent pubic/axillary hair: Suggests complete androgen insensitivity syndrome. 2
• Galactorrhea: Indicates hyperprolactinemia requiring pituitary imaging. 1, 2
• Headaches or visual changes: Suggests pituitary pathology requiring immediate MRI. 2
• Signs of eating disorder or significant weight loss: Requires multidisciplinary eating disorder team. 2

Common Pitfalls to Avoid

• Do not assume amenorrhea in athletes is benign: Other pathology must be excluded even when clinical picture suggests functional hypothalamic amenorrhea. 2
• Do not prescribe oral contraceptives as first-line therapy: This masks the problem without addressing underlying causes and provides false reassurance. 2
• Do not overlook eating disorders: Adolescents frequently minimize or deny disordered eating behaviors—direct questioning about specific behaviors is necessary. 2
• Do not delay bone density assessment: DXA scanning is indicated if amenorrhea extends beyond 6 months, regardless of age, as 90% of peak bone mass is attained by age 18. 2
• Do not forget to discontinue hormone replacement therapy: If patient is on any hormonal therapy, discontinue at least 2 months before laboratory evaluation to avoid falsely reassuring results. 3

When to Refer

Immediate referral to endocrinology and/or gynecology is indicated for:

• Prepubertal females with no signs of puberty by age 13 years with elevated FSH levels 5
• Primary amenorrhea by age 16 years in presence of other pubertal development 5, 2, 3
• Failure to initiate or progress through puberty for ≥12 months 5, 3
• Confirmed primary ovarian insufficiency (two elevated FSH values) 2, 3
• Suspected pituitary pathology or structural abnormalities 2, 3