Laboratory Testing for Perimenopause Assessment
Clinical history is the most appropriate method for assessing perimenopausal status, and routine hormone testing provides little useful information because hormone levels fluctuate markedly during this transition. 1, 2
When Laboratory Testing Is Indicated
Laboratory evaluation should be reserved for specific clinical scenarios rather than routine screening:
Measure FSH, LH, estradiol, and prolactin only when clinically indicated – for example, when excluding other causes of menstrual irregularity such as thyroid disease, hyperprolactinemia, or premature ovarian insufficiency. 3
Rule out pregnancy first with a urine or serum pregnancy test before pursuing any hormonal evaluation in women with amenorrhea or irregular cycles. 4
Check TSH to identify thyroid dysfunction as a reversible cause of menstrual irregularity, since both hypothyroidism and hyperthyroidism disrupt cycles. 4
Why Routine FSH Testing Is Unreliable in Perimenopause
The perimenopausal transition is characterized by extreme hormonal variability that makes single measurements meaningless:
FSH levels fluctuate markedly during perimenopause, with both ovulatory cycles (showing minimal FSH elevation) and anovulatory cycles (showing markedly elevated FSH) occurring unpredictably even after entering the late transition. 2
No specific endocrine marker distinguishes early from late menopausal transition, confirming that measurements of FSH or estradiol are unreliable for staging an individual woman's proximity to menopause. 2
Estradiol levels may be maintained or even elevated during much of the perimenopausal transition despite rising FSH, due to compensatory ovarian stimulation. 1, 2
The average duration of perimenopause is approximately 5 years, during which hormone levels show increasing variability rather than orderly progressive decline. 1
Clinical Diagnosis Without Laboratory Testing
Base the diagnosis on menstrual pattern changes and symptoms:
Early perimenopause is defined by variable cycle length (>7 days different from normal) with maintained regular cycles overall. 1
Late perimenopause is characterized by amenorrhea intervals of ≥60 days between cycles. 1
Vasomotor symptoms (hot flashes, night sweats) tend to be most frequent around the time of final menses and correlate with greater hormonal variability. 3, 5
Special Circumstances Requiring Laboratory Testing
Certain clinical contexts do warrant hormonal assessment:
For women on tamoxifen or after chemotherapy, FSH is not a reliable marker of menopausal status; serial estradiol levels are more useful to determine return of ovarian function. 3
If considering aromatase inhibitor therapy in breast cancer patients with therapy-induced amenorrhea, serial FSH and/or estradiol measurements are needed to ensure postmenopausal status, since amenorrhea alone is unreliable. 3
When premature ovarian insufficiency is suspected (age <40 with amenorrhea), measure FSH and confirm with repeat testing 4 weeks later; two elevated values (>40 mIU/mL) are required for diagnosis. 4
Elevated prolactin (>20 μg/L) warrants evaluation for pituitary adenoma or medication effects if galactorrhea is present. 4
Common Pitfalls to Avoid
Do not order FSH/estradiol panels routinely in women aged 45–55 with typical perimenopausal symptoms and menstrual irregularity, as results will not change management and may be misleading due to cycle-to-cycle variability. 1, 2
Do not assume a single elevated FSH confirms menopause during the transition, since ovulatory cycles with normal FSH can still occur even after prolonged amenorrhea. 2
Do not use hormone levels to time hormone therapy initiation; instead, base treatment decisions on symptom severity and quality of life impact. 3
Avoid drawing prolactin after breast examination, stress, or sexual activity, as these cause transient elevations; obtain a morning resting sample instead. 4