Laboratory Evaluation for Amenorrhea
All patients presenting with amenorrhea require an initial pregnancy test followed by measurement of FSH, LH, TSH, and prolactin levels to systematically identify the underlying cause. 1, 2
Initial Mandatory Laboratory Tests
The first-line laboratory workup must include:
Pregnancy test (urine or serum β-hCG) - This is the absolute first test that must be performed before any other hormonal evaluation, as pregnancy is the most common cause of amenorrhea 1, 3, 4
Follicle-stimulating hormone (FSH) - Elevated levels (>40 mIU/mL) indicate primary ovarian insufficiency and require confirmation with repeat testing 4 weeks later 1, 2
Luteinizing hormone (LH) - An LH/FSH ratio >2 strongly suggests polycystic ovary syndrome (PCOS) 5, 1, 2
Thyroid-stimulating hormone (TSH) - Identifies thyroid dysfunction as a reversible cause of amenorrhea 5, 1
Prolactin - Elevated levels (>20 μg/L) suggest hyperprolactinemia, which may indicate a pituitary adenoma or medication effect 5, 6
Additional Hormonal Testing Based on Clinical Context
Estradiol levels should be measured when functional hypothalamic amenorrhea (FHA) is suspected, as low levels indicate hypoestrogenism 5, 1
Progesterone levels (measured mid-luteal phase) help determine ovulatory status - levels <6 nmol/L indicate anovulation, commonly seen in PCOS, hypothalamic amenorrhea, or hyperprolactinemia 5
Testosterone and androstenedione should be measured when clinical signs of hyperandrogenism are present (hirsutism, acne) - testosterone >2.5 nmol/l suggests PCOS or valproate use 5
DHEA-S (dehydroepiandrosterone sulfate) is indicated when androstenedione is elevated (>10.0 nmol/l) to rule out adrenal or ovarian tumors 5
Timing Considerations for Laboratory Testing
Blood samples for FSH, LH, and testosterone should ideally be drawn between days 3-6 of the menstrual cycle (or at any time in amenorrheic patients) 5. For progesterone assessment, blood must be drawn during the mid-luteal phase according to the menstrual cycle 5.
Critical pitfall: FSH is not a reliable marker of menopausal status in patients with prior chemotherapy, pelvic radiation, or those taking tamoxifen 5. In these populations, serial estradiol levels are more useful for determining ovarian function 5.
Imaging Studies
Pelvic ultrasonography (preferably transvaginal) is indicated when clinical features or hormonal tests suggest ovarian pathology, such as PCOS (>10 peripheral cysts of 2-8 mm diameter) 5, 1, 2
Endometrial thickness assessment via ultrasound helps differentiate causes: thin endometrium (<5 mm) suggests estrogen deficiency while thick endometrium (>8 mm) suggests chronic anovulation with unopposed estrogen 1, 2
Pituitary MRI should be obtained if prolactin is elevated or if galactorrhea is present to rule out a pituitary adenoma 5
Special Population Considerations
In female athletes, the evaluation must specifically assess for the Female Athlete Triad by documenting weight changes, eating patterns, and exercise habits 5, 2. In this population with energy deficiency-related amenorrhea, bone mineral density testing via DXA should be obtained 5.
In cancer survivors, FSH and estradiol should be measured, but hormone replacement therapy must be discontinued prior to laboratory evaluation 5, 2. Anti-Müllerian hormone (AMH) and inhibin may provide additional information on ovarian status but are not reliable alone 5.
In patients with primary ovarian insufficiency (confirmed by two FSH levels >40 mIU/mL taken 4 weeks apart), karyotype testing should be performed if the patient is under age 40 to identify Turner syndrome or other chromosomal abnormalities 1, 2