What initial laboratory tests should be ordered for a 20-year-old patient (Pt) complaining of amenorrhea (not having a menstrual period) for over a year?

Laboratory Evaluation for Amenorrhea in a 20-Year-Old Patient

The initial laboratory workup for a 20-year-old patient with amenorrhea for over a year should include pregnancy test, FSH, LH, TSH, prolactin, and estradiol levels. 1, 2

Initial Assessment

• Obtain a detailed menstrual history including age of menarche, previous regularity of cycles, and duration of amenorrhea 1
• Document medical history with attention to weight changes, eating patterns, exercise habits, and medication use 1
• Calculate BMI, as both low and high BMI can contribute to menstrual irregularities 1
• Assess for symptoms suggesting specific etiologies such as galactorrhea (hyperprolactinemia), hirsutism/acne (PCOS), or vasomotor symptoms (ovarian insufficiency) 3

Essential Laboratory Tests

• Pregnancy test - This is the mandatory first step to exclude pregnancy as a cause of amenorrhea 1, 4
• FSH and LH levels - Help distinguish between hypothalamic, pituitary, and ovarian causes:
  • Elevated FSH (>35 IU/L) suggests primary ovarian insufficiency 3
  • LH/FSH ratio >2 suggests polycystic ovary syndrome (PCOS) 3, 1
  • Low/normal FSH and LH may indicate hypothalamic amenorrhea 2
• TSH - To evaluate for thyroid dysfunction, which can cause menstrual irregularities 3, 1
• Prolactin - Elevated levels (>20 μg/L) suggest hyperprolactinemia, which may be caused by medications, pituitary adenoma, or other conditions 3, 1
• Estradiol - Low levels may confirm hypoestrogenic state 1, 2

Additional Tests Based on Initial Results

• If clinical features or hormonal tests suggest ovarian pathology, pelvic ultrasonography is indicated 3, 1
  • Transvaginal ultrasound is more sensitive than transabdominal for identifying structural abnormalities 3
• If hirsutism or other signs of hyperandrogenism are present, consider testing testosterone and androstenedione levels 3
• If hyperprolactinemia is detected, pituitary MRI may be needed to evaluate for pituitary adenoma 3
• Consider karyotype analysis if primary amenorrhea or premature ovarian insufficiency is suspected 2, 5

Common Pitfalls to Avoid

• Don't assume that a negative pregnancy test rules out all serious pathology; further investigation is necessary 4
• Remember that amenorrhea is a symptom, not a diagnosis, and requires identification of the underlying cause 6
• Be aware that patients with hypothalamic amenorrhea should be evaluated for disordered eating and are at risk for decreased bone density 1, 5
• Consider that certain medications, including antipsychotics, antiepileptics, and hormonal contraceptives, can cause amenorrhea 1

When to Refer

• Refer to gynecology/endocrinology if laboratory testing reveals significant abnormalities 1
• Consider referral if there is concern for an eating disorder or Female Athlete Triad 1
• Immediate referral is warranted for patients with primary ovarian insufficiency or signs of central nervous system pathology 2

This systematic approach to laboratory evaluation will help identify the underlying cause of amenorrhea and guide appropriate management to address both the immediate symptoms and potential long-term health implications.