What does a low Follicle-Stimulating Hormone (FSH) level with normal testosterone levels indicate in a male in his 50s?

Low FSH with Normal Testosterone in a Male in His 50s

A low FSH with normal testosterone in a male in his 50s most likely indicates secondary (central) hypogonadism affecting the pituitary-hypothalamic axis, though the normal testosterone suggests the condition may be subclinical or compensated. This pattern warrants further evaluation to identify the underlying cause, particularly if the patient has symptoms of hypogonadism.

Understanding the Hormonal Pattern

The combination of low FSH with normal testosterone is inconsistent with primary testicular failure and points to a central (hypothalamic-pituitary) issue. 1

• In primary hypogonadism (testicular failure), you would expect low testosterone with elevated FSH and LH as the pituitary attempts to compensate for testicular dysfunction 2
• In secondary hypogonadism, both testosterone and gonadotropins (FSH/LH) are low or inappropriately normal 1
• The fact that testosterone remains normal despite low FSH suggests either:
  • Early/partial pituitary-hypothalamic dysfunction where LH secretion is preserved but FSH is selectively suppressed
  • A compensated state where remaining testicular function maintains adequate testosterone production 3

Clinical Significance in Men Over 50

In men over 50, this pattern requires careful evaluation because it may represent age-related changes, obesity-related hormonal suppression, or underlying pituitary pathology. 1

• Obesity is a major confounder in this age group and can suppress gonadotropin secretion through increased aromatization of testosterone to estradiol in adipose tissue, leading to negative feedback on the pituitary 1
• Age-related decline in testosterone typically shows low-normal testosterone with normal or low gonadotropins, not isolated low FSH 4, 5
• The normal testosterone level argues against clinically significant hypogonadism unless free testosterone is low due to decreased sex hormone-binding globulin 1

Recommended Diagnostic Approach

Repeat morning (8-10 AM) measurements of total testosterone, free testosterone, LH, and FSH on at least one additional occasion to confirm the pattern. 1

• Measure free testosterone by equilibrium dialysis and sex hormone-binding globulin, as total testosterone can be misleadingly normal in obesity when free testosterone is actually low 1
• Obtain LH levels to determine if both gonadotropins are suppressed or if FSH is selectively low 1, 3
• If the pattern persists with low FSH and low or inappropriately normal LH, further evaluation for secondary hypogonadism is warranted 1

Further Evaluation for Secondary Hypogonadism

If confirmed low gonadotropins are present, measure serum prolactin and iron saturation, and consider pituitary function testing and MRI of the sella turcica to identify hypothalamic-pituitary pathology. 1

• Hyperprolactinemia can suppress gonadotropin secretion and is a treatable cause 1
• Hemochromatosis (elevated iron saturation) can cause pituitary dysfunction 1
• Pituitary tumors, infiltrative diseases, or prior radiation/trauma should be excluded with imaging if biochemical testing suggests central hypogonadism 1
• Consider medication review for drugs that suppress gonadotropin secretion (opioids, glucocorticoids, anabolic steroids) 6

Assessment of Clinical Hypogonadism

Determine whether the patient has symptoms of hypogonadism before considering treatment, as biochemical abnormalities alone do not warrant testosterone replacement. 1, 4

• Key symptoms to assess include: decreased libido, erectile dysfunction, decreased energy, reduced muscle mass, hot flashes, and mood changes 1
• The American College of Physicians recommends against initiating testosterone treatment solely to improve energy, vitality, or physical function in men with age-related low testosterone 1
• Treatment should only be considered if free testosterone is frankly low on repeated testing AND the patient has clear symptoms of hypogonadism after completing the workup to exclude other causes 1

Common Pitfalls to Avoid

• Do not assume normal total testosterone excludes hypogonadism—always check free testosterone, especially in obese men 1
• Do not diagnose secondary hypogonadism based on a single FSH measurement—hormonal variability requires confirmation 1
• Do not overlook obesity as a reversible cause—weight loss can normalize the hypothalamic-pituitary-gonadal axis 1
• Do not initiate testosterone replacement without completing the evaluation for pituitary pathology—treating secondary hypogonadism without identifying the cause can mask serious conditions like pituitary tumors 1