LH and FSH in men are the two pituitary hormones that reveal whether low testosterone starts in the testicles or in the brain. Measured alongside a morning testosterone level, they split low T into two very different diagnoses: primary hypogonadism, where the testicles themselves have stopped producing, and secondary hypogonadism, where the signal from above never arrives. That single distinction decides whether testosterone replacement is the obvious answer, whether fertility can be protected, and whether something reversible is hiding behind the number.
Most men who walk into a clinic with fatigue, low libido and stubborn belly fat get one test: total testosterone. If it comes back low, they get a prescription. It is a fast route to feeling better, and it skips the question that actually matters — why is it low?
What LH and FSH Actually Do
Testosterone production runs on a chain of command. The hypothalamus releases GnRH in pulses. The pituitary answers by secreting luteinising hormone (LH) and follicle-stimulating hormone (FSH). LH travels to the Leydig cells in the testicles and tells them to make testosterone. FSH goes to the Sertoli cells and drives sperm production.
The loop closes on itself. When testosterone rises, the hypothalamus and pituitary throttle back. When testosterone falls, they push harder. That feedback mechanism is why the gonadotropins are so diagnostically useful: they tell you which end of the chain is broken. A healthy pituitary responding to failing testicles will shout louder. A failing pituitary stays quiet no matter how low testosterone drops.
LH and FSH in Men: The Four Patterns Worth Knowing
Interpreted together with a testosterone level, LH and FSH in men fall into one of four patterns. Nearly every result you will see lands in one of these buckets.
Low testosterone with high LH and FSH
This is primary hypogonadism, sometimes called hypergonadotropic hypogonadism. The pituitary is working fine — it is screaming at testicles that cannot respond. Causes include Klinefelter syndrome, mumps orchitis, testicular trauma, chemotherapy or radiation, undescended testicles in childhood, and simple age-related Leydig cell decline. Mayo Clinic lists testicular injury and genetic conditions among the most common culprits. There is no restarting a testicle that has failed, so replacement therapy is usually the appropriate route.
Low testosterone with low or inappropriately normal LH and FSH
This is secondary hypogonadism, and it is the pattern that most often gets missed. Testosterone is low, but the gonadotropins sit in the middle of the reference range — which sounds reassuring until you remember they should be elevated. A normal LH next to a testosterone of 220 ng/dL is not normal; it is a pituitary that has stopped doing its job.
The list of causes here is long and, crucially, often reversible: obesity, obstructive sleep apnoea, opioid painkillers, chronic corticosteroids, past anabolic steroid use, severe illness, poorly controlled diabetes, and pituitary tumours. A prolactin-secreting adenoma is the classic example — one reason prolactin belongs on the same panel. Treat the cause and testosterone frequently recovers on its own.
Normal testosterone with isolated high FSH
Here the Leydig cells are fine but the sperm-producing machinery is damaged. Testosterone and LH look unremarkable while FSH climbs, because the Sertoli cells have stopped producing inhibin B and the brake is off. Men usually discover this during a fertility workup rather than a low-T workup. As Cleveland Clinic explains, FSH is the more sensitive marker of spermatogenesis, which is why a semen analysis should follow.
Everything suppressed
If a man is already on exogenous testosterone, LH and FSH will be at or near the floor. That is expected physiology, not pathology. It also means the window for baseline testing closes the day treatment starts — measure first, treat second.
Getting the Test Right
Timing matters more than most men realise. LH and FSH in men are secreted in pulses, roughly every 60 to 90 minutes, so a single LH value can swing considerably. Draw blood between 7am and 10am, when testosterone peaks and the pattern is most interpretable. Fasting is not strictly required, but it makes little difference to convenience since a full hormone blood test panel is usually drawn at the same time.
A meaningful panel includes total testosterone, free testosterone, SHBG, LH, FSH, prolactin and estradiol. Abnormal results should always be repeated on a second morning before anyone commits to a diagnosis. Acute illness, a night of bad sleep or a hard training block can all push a single reading out of range.
How LH and FSH Change the Treatment Plan
This is where the test earns its keep. For a man with primary hypogonadism, the testicles are not coming back, and testosterone replacement therapy is the straightforward answer. Fertility, if it matters, needs a separate conversation and often sperm banking.
For secondary hypogonadism, the picture is more open. The pituitary axis is intact, which means it can sometimes be restarted. Weight loss, treating sleep apnoea, tapering opioids or addressing a prolactinoma can restore levels without any lifelong prescription. And if a man wants children in the near future, hCG alongside or instead of testosterone therapy can keep the testicles working rather than shutting them down.
Interpreting LH and FSH in men also protects against the opposite error: treating a man whose symptoms are not hormonal at all. Fatigue, low mood and poor libido overlap heavily with thyroid disease, depression, anaemia and sleep disorders. If testosterone is genuinely borderline and the gonadotropins are unremarkable, the signs of low testosterone may be pointing somewhere else entirely.
Test Before You Treat
Two extra markers on a blood form cost very little and change the plan more often than most men expect. If you are considering hormone therapy — or you have already been told your testosterone is low without anyone explaining why — ask for LH and FSH in men to be included on the panel before you start. Nova Men’s Health runs full hormone panels and physician-led consultations across India. Book a consultation and find out what your numbers are actually telling you.