Laboratory Tests for Irregular Menses
For patients with irregular menses, laboratory testing should include hemoglobin, luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin, estradiol, thyroid function tests (T4, TSH), pregnancy test, and androgen profile. 1
Initial Laboratory Evaluation
Essential First-Line Tests
- Complete Blood Count (CBC): To assess for anemia which may be associated with menorrhagia
- Pregnancy Test: To rule out pregnancy as a cause of missed periods
- Thyroid Function Tests:
- TSH
- Free T4
- These tests are critical as thyroid dysfunction is a common cause of menstrual irregularity 2
- Reproductive Hormone Panel:
- Luteinizing Hormone (LH)
- Follicle Stimulating Hormone (FSH)
- Estradiol
- Prolactin
- Androgen profile (Total testosterone, Free testosterone, DHEAS)
Timing Considerations
- Hormonal testing should be performed between days 3-6 of the menstrual cycle when possible 1
- Any hormone replacement therapy should be discontinued prior to laboratory evaluation to avoid false results 3
- For prolactin, measurements should be taken in the morning in a resting state (not post-seizure or post-stress) 1
Second-Line Tests Based on Clinical Suspicion
For Suspected PCOS
- LH/FSH ratio (ratio >2 suggests PCOS) 1, 3
- Fasting glucose and insulin (to assess insulin resistance)
- Consider transvaginal ultrasound to evaluate ovarian morphology 3
For Suspected Premature Ovarian Failure
- Repeat FSH measurements (>35 IU/L on two occasions at least one month apart confirms diagnosis) 3
- Anti-Müllerian hormone (AMH) as an adjunctive test (not for primary surveillance) 3
For Suspected Hyperprolactinemia
- If prolactin >20 μg/L, consider pituitary imaging 1, 4
- Rule out hypothyroidism which can cause secondary hyperprolactinemia 5
Interpretation of Key Laboratory Values
| Laboratory Test | Abnormal Finding | Clinical Significance |
|---|---|---|
| FSH | >35 IU/L | Suggests ovarian failure [3] |
| LH/FSH ratio | >2 | Suggests PCOS [1,3] |
| Prolactin | >20 μg/L | Suggests hyperprolactinemia [1] |
| Progesterone | <6 nmol/L in luteal phase | Suggests anovulation [3] |
| TSH | Elevated or decreased | Suggests thyroid dysfunction [2] |
| Testosterone | >2.5 nmol/L | Suggests hyperandrogenism [3] |
Additional Considerations
- Imaging Studies: Consider pelvic ultrasound if clinical features or hormonal tests suggest ovarian pathology 1
- Pituitary Imaging: MRI with contrast is indicated if prolactin is elevated or if multiple pituitary hormone abnormalities are present 1
- Endometrial Sampling: May be indicated in cases of prolonged abnormal bleeding to rule out endometrial pathology 1
Common Pitfalls to Avoid
- Relying on a single FSH measurement for diagnosing premature ovarian failure; two elevated measurements at least one month apart are required 3
- Testing during hormonal contraceptive use can lead to false results 3
- Overlooking thyroid dysfunction as a common and treatable cause of menstrual irregularity 2
- Failing to consider pregnancy as a cause of missed periods before extensive hormonal workup
- Not recognizing that stress, excessive exercise, and weight changes can cause functional hypothalamic amenorrhea, which is a diagnosis of exclusion 1
Remember that functional hypothalamic amenorrhea (FHA) is a diagnosis of exclusion, and comprehensive laboratory testing is essential to rule out other causes of menstrual irregularity before making this diagnosis 1.