FSH and LH Testing: Timing Requirements
For most clinical indications, FSH and LH should be collected in the morning (around 8 AM) to optimize accuracy, particularly for gonadotropin measurements, though the specific day of the menstrual cycle is more critical than time of day for menstruating women. 1
Timing Considerations by Clinical Context
Time of Day Requirements
- Morning collection (around 8 AM) is critical for accurate interpretation of hormone levels, particularly when assessing the hypothalamic-pituitary-gonadal axis, as this timing optimizes gonadotropin and sex hormone measurements 1
- Morning sampling is especially important when evaluating for hypogonadism, as testosterone levels show significant diurnal variation and should be taken in the morning 2
- For patients on immunotherapy or with suspected pituitary dysfunction, morning collection ensures optimal assessment of FSH, LH, and other pituitary hormones 1
Menstrual Cycle Timing (For Menstruating Women)
- FSH and LH should be collected during the early follicular phase (days 2-5 of the menstrual cycle) for baseline assessment 2, 3
- Mid-follicular phase sampling (around day 6) can be used to assess progressive changes in gonadotropin levels 4
- The timing within the menstrual cycle is more critical than time of day for menstruating women, as FSH and LH levels vary dramatically throughout the cycle 5
- A mid-cycle LH peak is a laboratory criterion for normal ovulatory cycles, so timing relative to ovulation matters for specific indications 5
Special Clinical Situations
For hypogonadism evaluation:
- In premenopausal women with menstrual irregularity or evidence of hypogonadism, FSH, LH, and estradiol should be assessed together to distinguish primary from secondary hypogonadism 2, 1
- Low gonadotropins with low sex hormones indicate central (pituitary) dysfunction, while high gonadotropins with low sex hormones indicate primary gonadal failure 1
For polycystic ovary syndrome (PCOS) diagnosis:
- FSH and LH should be measured in the follicular phase, as an LH to FSH ratio >2 is characteristic of PCOS 2
- In functional hypothalamic amenorrhea (FHA), the LH to FSH ratio is typically <1 in about 82% of patients 2
For fertility treatment monitoring:
- Sequential LH measurements may be used to time ovulation during artificial insemination or in vitro fertilization programs 3
- During ovulation induction therapy, FSH and LH can be monitored on alternate days to assess response 6
Common Pitfalls and Caveats
- Avoid single time-point measurements when investigating reproductive disorders, as sampling at only one time of day or one point in the cycle can lead to incorrect conclusions 2
- Do not collect samples during or immediately after corticosteroid administration when evaluating for hypophysitis, as steroids suppress the hypothalamic-pituitary axis and confound results 1
- For postmenopausal women or men, cycle timing is irrelevant, but morning collection remains optimal 2, 1
- Serum is preferred to plasma and should be stored frozen before assay if not processed immediately 3
- No special preservatives are needed for sample collection 3