Workup for Irregular Menses in an 18-Year-Old Non-Pregnant Female
The first-line workup requires a pregnancy test (already confirmed negative), followed by measurement of TSH, prolactin, FSH, and LH to identify the most common reversible and serious causes of menstrual irregularity in this age group. 1
Initial Laboratory Panel
The essential hormonal assessment includes:
- TSH measurement to identify thyroid dysfunction, which is a reversible cause of menstrual irregularity 1
- Prolactin level to screen for hyperprolactinemia (>20 μg/L suggests pituitary adenoma or medication effect) 1
- FSH and LH levels drawn at any time (since cycles are irregular) to differentiate between primary ovarian insufficiency and polycystic ovary syndrome 1
- LH/FSH ratio >2 strongly suggests PCOS, while elevated FSH (>40 mIU/mL) indicates primary ovarian insufficiency 1
Clinical History Elements to Document
Beyond basic menstrual history, specifically assess:
- Weight changes, eating patterns, and exercise habits to evaluate for Female Athlete Triad or functional hypothalamic amenorrhea 1
- BMI calculation is essential, as BMI >25 kg/m² associates with PCOS while BMI <18.5 kg/m² favors hypothalamic amenorrhea 1
- Medication use, particularly antipsychotics, antiepileptics, and hormonal contraceptives that can cause irregular menses 1
- Presence of galactorrhea, which mandates prolactin measurement and pituitary evaluation 1
- Hyperandrogenic signs including hirsutism, acne, or androgenetic alopecia that suggest PCOS 1
Physical Examination Priorities
- Tanner staging of breast and pubic hair development 1
- Thyroid examination to identify enlargement or nodules 1
- BMI and waist-to-hip ratio (>0.9 suggests truncal obesity and supports PCOS workup) 1
- Ferriman-Gallwey scoring if hirsutism is present 1
Additional Testing Based on Initial Results
If hyperandrogenic signs are present:
- Add total testosterone (>2.5 nmol/L suggests PCOS or valproate effect) 1
- Measure androstenedione (>10.0 nmol/L warrants investigation for adrenal or ovarian neoplasms) 1
- Check DHEA-S using age-adjusted thresholds to screen for non-classical congenital adrenal hyperplasia 1
If FSH is elevated (>40 mIU/mL):
- Repeat FSH in 4 weeks (two elevated values required for diagnosis of primary ovarian insufficiency) 1
- Karyotype analysis is recommended for women <40 years to detect Turner syndrome 1
If clinical picture suggests anovulation:
- Mid-luteal progesterone (<6 nmol/L confirms anovulation) 1
- Fasting glucose and insulin (glucose >7.8 mmol/L suggests diabetes; glucose/insulin ratio >4 indicates insulin resistance in PCOS) 1
Imaging Considerations
Pelvic ultrasonography is NOT routinely required for initial workup unless:
- Clinical features or hormonal tests suggest ovarian pathology 1
- Endometrial assessment is needed (thin endometrium <5 mm suggests estrogen deficiency; thick >8 mm suggests chronic anovulation) 1
- Transvaginal ultrasound is more sensitive than transabdominal for structural abnormalities 1
Critical Pitfalls to Avoid
- Never draw prolactin immediately after stress, breast examination, or sexual activity—obtain a morning resting sample 1
- Do not draw prolactin post-ictally—seizures cause transient elevation; wait at least 24 hours 1
- Avoid misdiagnosing functional hypothalamic amenorrhea with polycystic ovarian morphology as PCOS—FHA patients have low LH, low estradiol, thin endometrium, and LH/FSH ratio <1 despite ovarian appearance 1
- Refer for specialist evaluation if prolactin >100 μg/L, testosterone >5 nmol/L, rapid virilization occurs, or if there are headaches/visual disturbances 1
Unnecessary Tests at Initial Evaluation
The following are NOT needed for routine workup in a healthy 18-year-old 2:
- Pelvic examination (unless inserting IUD or fitting diaphragm)
- Cervical cytology or Pap smear
- Clinical breast examination
- HIV screening
- Lipid, glucose, liver enzyme panels (unless specific clinical indication)