LH and FSH
The Gonadotropins - Distinguishing Primary from Secondary Hypogonadism
Evidence grade 4 of 5, Strong. Read how the Atlas grades evidence.
The written rationale for this grade is still being prepared.
- FDA
- Pituitary hormone measurements run by immunoassay in CLIA labs.
Reference only. Not medical advice.
What can go wrong
A TRT prescription written off a low total-T number alone can mask a prolactinoma or other pituitary pathology (secondary hypogonadism) that LH/FSH would have flagged, and it will itself suppress LH/FSH and spermatogenesis. Once exogenous testosterone is on board, the gonadotropin picture is confounded and the diagnostic window is largely closed.
This is something to take to a clinician. The Atlas can tell you what is known about lh and fsh in general. It cannot tell you what is happening in your body, and the difference matters most for exactly the symptoms that bring people to this page.
Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are pituitary gonadotropins that drive testicular testosterone and sperm production. Their levels localize the lesion in a hypogonadal man. High LH/FSH with low testosterone = primary (testicular) hypogonadism, or hypergonadotropic. Low or inappropriately-normal LH/FSH with low testosterone = secondary (hypothalamic-pituitary) hypogonadism, or hypogonadotropic - which prompts a search for pituitary disease, hyperprolactinemia, opioids, or exogenous androgen suppression. This localization is a step the low-T marketplace usually omits.
The two numbers that tell you whether the problem is the testes or the brain.
What people take it for
What it is taken for. Approval, where it exists, covers only some of these.
How it works
Testosterone and inhibin normally feed back to suppress LH and FSH. When the testes fail (primary), feedback is lost and gonadotropins rise. When the hypothalamus or pituitary fails (secondary), the drive itself is deficient, so gonadotropins are low or fail to rise despite low testosterone. Because exogenous testosterone suppresses LH and FSH, a man on TRT or anabolic steroids shows low gonadotropins - a pattern indistinguishable at a glance from true secondary hypogonadism, which is diagnostically important.
The catch: skipping LH/FSH hides fixable and dangerous causes
Prescribing testosterone without checking LH and FSH can bury a treatable pituitary tumor, an opioid effect, or covert anabolic use, and it forecloses fertility-sparing options like hCG, clomiphene, or SERM therapy that are only appropriate in secondary hypogonadism. It also means the clinician cannot later tell whether suppressed gonadotropins reflect the disease or the therapy. Localization is cheap and consequential; the funnel skips it because it does not sell TRT faster.
What it does to fertility
Because exogenous testosterone suppresses LH and FSH and shuts down spermatogenesis, checking gonadotropins before therapy is essential for men who want to preserve fertility; secondary hypogonadism specifically permits hCG/SERM alternatives.
What people get wrong
Often saidIf testosterone is low, the cause doesn't change the treatment
ActuallyIt changes it entirely. Secondary hypogonadism can signal a pituitary tumor and allows fertility-sparing therapy; primary does not. LH/FSH make that distinction.
Often saidLow LH just means low testosterone
ActuallyLow LH/FSH with low T points to the brain, not the testes - and could be opioids, a prolactinoma, or hidden exogenous androgen use.
Who profits, and who pushes back
Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.
At a glance
- LH/FSH source
- Anterior pituitary gonadotroph cells
- Primary hypogonadism
- Low T + HIGH LH/FSH (testicular failure)
- Secondary hypogonadism
- Low T + LOW or inappropriately-normal LH/FSH
- Key trigger of secondary
- Pituitary tumor, hyperprolactinemia, opioids, obesity, exogenous androgens
- Why it matters
- Changes the workup and whether fertility can be preserved
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about LH and FSH. A short entry is not a safe entry.
- Timeline. We have not built the dated record of research and regulatory events.
- Cost and market. We have not documented what it sells for or who sells it.
- Supply chain. We have not mapped where it is made.
- Who uses it. We have not documented the user groups.
- What could change. No forward-looking summary yet.
- How it compares. We have not set it against the alternatives.
- Children and teenagers. We have not checked what is known about younger people.
- Where we land. We have not taken a position on this yet.
Sources
The studies below are named and described, but not linked. You cannot open them from here and check our reading against them, which means this page is our summary of the literature rather than a document you can verify. Weigh it accordingly until the links exist.
The studies that matter
Bhasin et al., Endocrine Society guideline2018
Recommends measuring LH and FSH to distinguish primary from secondary hypogonadism once low T is confirmed
Basaria, Male hypogonadism, Lancet2014
Reviewed the gonadotropin-based classification and its implications for etiology and fertility
Male hypogonadism, Merck Manual / Endotextcurrent
Codifies high LH/FSH = primary, low/normal LH/FSH = secondary as the diagnostic pivot