What laboratory tests should be ordered for a patient presenting with irregular menstrual periods?

Laboratory Tests for Irregular Menstrual Periods

For patients presenting with irregular menstrual periods, the recommended initial laboratory evaluation should include FSH, LH, estradiol, prolactin, and TSH. 1

Initial Laboratory Assessment

The following tests should be ordered for the initial evaluation of irregular menstrual periods:

• First-line tests:

  • Follicle-stimulating hormone (FSH)
  • Luteinizing hormone (LH)
  • Estradiol
  • Prolactin
  • Thyroid-stimulating hormone (TSH)

• Additional tests based on clinical suspicion:

  • Complete blood count (to assess for anemia)
  • Testosterone (if signs of hyperandrogenism)
  • Hemoglobin A1c or fasting glucose/insulin (if PCOS suspected)

Expanded Laboratory Evaluation

If the initial workup is inconclusive or specific conditions are suspected, consider:

• For suspected PCOS:

  • LH:FSH ratio (>2 suggests PCOS)
  • Testosterone (>2.5 nmol/l is abnormal)
  • Androstenedione (>10.0 nmol/l is abnormal)
  • DHEAS (Age 20-29 >3800 ng/ml, Age 30-39 >2700 ng/ml)
  • Fasting glucose/insulin ratio 1

• For suspected thyroid dysfunction:

  • Free T4 (if TSH is abnormal) 1, 2

• For suspected premature ovarian failure:

  • FSH (>35 IU/l indicates ovarian failure) 3, 1

Imaging Studies

• Pelvic/transvaginal ultrasound: Recommended to evaluate ovarian morphology and rule out structural anomalies 1

  • For PCOS diagnosis: Look for ≥20 follicles per ovary and/or ovarian volume ≥10ml

• Brain MRI with contrast: Indicated if prolactin is elevated or if multiple pituitary hormone abnormalities are present 1

Specialized Testing

• Bone mineral density (DXA): Consider if amenorrhea persists >6 months to evaluate bone health 1

• Anti-Müllerian hormone (AMH): Emerging as a useful marker for ovarian reserve assessment, particularly in patients with history of gonadotoxic therapy 3

Clinical Pearls and Pitfalls

• Pitfall: Assuming anovulatory cycles in adolescents without proper evaluation. While common in the first 2-3 years post-menarche, pathological causes should still be ruled out 4, 5

• Pitfall: Missing thyroid dysfunction. While hypothyroidism is less frequently associated with menstrual disturbances than previously thought (23.4% of hypothyroid patients have irregular cycles), it remains an important reversible cause 6

• Caveat: Laboratory values must be interpreted in context of the patient's age and menstrual history. The LH:FSH ratio is typically <1 in 82% of patients with functional hypothalamic amenorrhea but >2 in PCOS 1

• Important note: Irregular menstruation is an important health indicator associated with various conditions including metabolic syndrome, coronary heart disease, type 2 diabetes, and rheumatoid arthritis 7

By following this structured approach to laboratory testing for irregular menstrual periods, clinicians can efficiently identify underlying causes and implement appropriate management strategies to improve patient outcomes.