FSH and LH Measurement in Pituitary Adenoma Evaluation
FSH and LH should be measured during the early follicular phase (days 3-6) of the menstrual cycle when evaluating a pituitary adenoma. 1
Rationale for Early Follicular Phase Measurement
- The Endocrine Society recommends measuring FSH and LH during the early follicular phase (days 3-6) of the menstrual cycle for the most accurate assessment of pituitary function in women 1
- During the early follicular phase, gonadotropin levels are relatively stable, providing a reliable baseline for assessment 2
- This timing minimizes the confounding effects of the mid-cycle LH surge and the fluctuations that occur during the luteal phase 3
- Morning measurements (around 8 am) are preferred to account for diurnal variations in hormone levels 1
Physiological Considerations
- FSH and LH levels vary significantly throughout the menstrual cycle, with a small early follicular phase rise in FSH, followed by relatively constant levels until mid-cycle 2
- A mid-cycle rise of FSH occurs coincidentally with the LH ovulatory peak in most women 2
- During the luteal phase, FSH levels are relatively constant but lower than during the follicular phase, making this phase less optimal for baseline assessment 2, 3
- The pulsatile nature of LH and FSH secretion can affect measurement accuracy, with LH pulse frequency increasing during the follicular phase 3
Interpretation of Results in Pituitary Adenoma Context
- Normal early follicular phase values for FSH range from 2.4-10 IU/L and for LH from 1.6-9.3 IU/L 4
- In pituitary adenomas, the most commonly affected pituitary axis is the GH axis (61-100%), followed by hypogonadism (36-96%) 1
- FSH-secreting pituitary adenomas may present with normal or elevated FSH levels despite pituitary dysfunction 4
- An LH/FSH ratio >2 may indicate polycystic ovary syndrome, which can be associated with pituitary disorders 1
- FSH >35 IU/L and LH >11 IU/L may indicate primary ovarian failure rather than pituitary pathology 1
Comprehensive Evaluation Approach
- A complete hormone panel for suspected pituitary adenomas should include not only FSH and LH but also prolactin, thyroid function tests, adrenal function assessment, gonadal hormones, and IGF-1 1
- For increased accuracy, consider calculating an average based on three estimations taken 20 minutes apart to account for the pulsatile nature of hormone secretion 1, 3
- Dynamic pituitary assessment of possible hypofunction and hyperfunction of other anterior pituitary hormones should be offered to patients with suspected pituitary adenomas 5
Special Considerations
- Age-related changes in FSH and LH should be considered when interpreting results, as FSH levels tend to increase after age 43 even in women with regular cycles 6
- Hormone measurements during use of hormonal contraceptives may mask underlying abnormalities and should be interpreted with caution 7
- In patients with pituitary adenomas, co-secretion of other hormones (particularly prolactin) is common and may affect the interpretation of results 5
By measuring FSH and LH during the early follicular phase, clinicians can obtain the most reliable baseline assessment of pituitary function, which is crucial for the accurate diagnosis and management of pituitary adenomas.