From the Guidelines
Low Follicle-Stimulating Hormone (FSH) in males is primarily caused by hypothalamic or pituitary disorders, and in the context of azoospermia, obstructive azoospermia is suspected when FSH levels are usually less than approximately 7.6 IU/L, as indicated in the 2024 AUA/ASRM guideline 1. When evaluating low FSH in males, it's essential to consider the underlying causes, which can include pituitary tumors, genetic conditions, head trauma, infiltrative diseases, and certain medications.
- Key factors to consider in the diagnosis of low FSH include:
- Physical examination findings, such as testes size and epididymides condition
- Semen analysis results, including sperm concentration, motility, and morphology
- Hormone levels, particularly FSH and luteinizing hormone (LH)
- Medical history, including any previous illnesses, injuries, or medications In the context of azoospermia, obstructive azoospermia is more likely when FSH levels are less than 7.6 IU/L, and the testes are of normal size, with fully descended and bilaterally dilated and/or indurated epididymides 1. It's crucial to distinguish between obstructive and non-obstructive azoospermia, as the treatment approaches differ significantly.
- Non-obstructive azoospermia is often associated with:
- Elevated FSH levels (>7.6 IU/L)
- Testicular atrophy
- Impaired sperm production
- Genetic abnormalities, such as Klinefelter syndrome or Y-chromosome microdeletions In contrast, obstructive azoospermia is typically characterized by low FSH levels, normal testes size, and the presence of dilated epididymides, with or without absence of the vas deferens 1. Accurate diagnosis and treatment of the underlying cause of low FSH are essential to improve fertility outcomes and overall quality of life for affected males.
From the Research
Causes of Low FSH in Males
Low Follicle-Stimulating Hormone (FSH) in males can be caused by several factors, including:
- Hypogonadotropic hypogonadism (HH), a condition characterized by a dysfunction in the hypothalamus and/or the pituitary gland, leading to low or inappropriately normal gonadotropin levels along with low total testosterone levels 2
- Pituitary dysfunction, which can be caused by various factors such as tumors, trauma, or infections, leading to impaired gonadotropin secretion 3
- Feedback inhibition of gonadotropins by testosterone, which can suppress FSH levels in men with hypogonadotropic hypogonadism 4
- Functional hypogonadotropic hypogonadism (FHH), a non-classical form of HH characterized by low-normal gonadotropin levels that are inadequate for testosterone levels 5
Associated Conditions
Low FSH in males can be associated with various conditions, including:
- Primary hypogonadism, characterized by elevated FSH levels and low testosterone levels 6
- Secondary hypogonadism, characterized by low or inappropriately normal FSH levels and low testosterone levels 5
- Pituitary tumors, such as microprolactinoma or macroprolactinoma, which can cause pituitary dysfunction and lead to low FSH levels 3
- Hypothalamic-pituitary disease or injury, which can disrupt the normal feedback mechanism between testosterone and gonadotropins 4
Diagnostic Considerations
Diagnosing the cause of low FSH in males requires a comprehensive evaluation, including:
- Measurement of FSH and testosterone levels 6, 4
- Evaluation of pituitary function and potential reversible causes in the hypothalamus-pituitary axis 3
- Pituitary magnetic resonance imaging (MRI) to rule out pituitary tumors or other abnormalities 3
- Assessment of semen analysis parameters, such as sperm concentration and morphology, to evaluate spermatogenesis 6