Normal Follicle-Stimulating Hormone (FSH) Levels
Normal FSH levels vary by age, sex, and reproductive status, with elevated levels (>40 IU/L) indicating primary ovarian insufficiency/failure or menopause, while levels >4.5 IU/L may be associated with abnormal semen parameters in men. 1, 2
Normal FSH Ranges
Women
- Premenopausal women (during menstrual cycle):
- Postmenopausal women: >40 IU/L 1
Men
- Adult males: 1.4-18.1 IU/L (traditional range)
- However, FSH levels >4.5 IU/L may indicate abnormal semen parameters 2
Children
- Prepubertal children: <4 IU/L
- During puberty: Gradually increases to adult levels 4
Clinical Significance of FSH Levels
Elevated FSH Levels (Women)
- >40 IU/L: Diagnostic of premature ovarian insufficiency (POI) or menopause 1
- >10 IU/L: May indicate diminished ovarian reserve, especially in women under 40 3
Elevated FSH Levels (Men)
- >4.5 IU/L: Associated with abnormal sperm morphology and concentration 2
- >7.5 IU/L: Five to thirteen-fold higher risk of abnormal semen quality compared to men with FSH <2.8 IU/L 2
Low FSH Levels
- May indicate:
- Hypogonadotropic hypogonadism
- Pituitary dysfunction
- Hypothalamic disorders 4
Timing of FSH Testing
- Women: FSH should be measured between days 2-4 of the menstrual cycle for accurate assessment of ovarian reserve 1
- Men: No specific timing required, but morning samples are preferred for consistency 4
FSH in Relation to Other Hormones
FSH:LH Ratio
- LH:FSH >2: Suggestive of polycystic ovary syndrome (PCOS)
- LH:FSH ≤1: Suggestive of functional hypothalamic amenorrhea (FHA) 1
Testosterone:FSH Ratio in Men
- Decreasing testosterone/FSH ratio correlates with higher probability of abnormal semen parameters 2
Clinical Applications
Fertility Assessment
- FSH is a key marker for ovarian reserve in women and spermatogenesis in men
- However, FSH is considered a relatively late marker of diminished ovarian reserve 3
- Anti-Müllerian hormone (AMH) may be a more sensitive early marker of ovarian reserve 1
Diagnosis of Hypogonadism
- In men with sperm concentration <10 million/mL, endocrine evaluation including serum testosterone and FSH is recommended 4
- In women with irregular menses or amenorrhea, FSH along with LH and estradiol helps differentiate between primary and secondary hypogonadism 1
Important Considerations
- FSH levels should be interpreted in the context of clinical presentation and other hormonal parameters
- Laboratory reference ranges may vary slightly between institutions and assay methods 5
- A single elevated FSH measurement should be confirmed with repeat testing, especially in women 1
- FSH bioactivity may not always correlate perfectly with immunoassay measurements, particularly during the mid-to-late luteal phase of the menstrual cycle 6
FSH is a crucial hormone in reproductive health assessment, but its interpretation requires consideration of age, sex, reproductive status, and other hormonal parameters for accurate clinical decision-making.