What Your LH Level Reveals About Your Testosterone and Fertility
Part 2 of the SwimScore Hormone Series
When men think about hormones and fertility, testosterone is usually the first thing that comes to mind. LH — luteinizing hormone — tends to get overlooked. That's a shame, because your LH level tells you something that a testosterone test alone cannot: whether your body is actually producing testosterone where it matters most for making sperm.
That distinction is more important than most people realize. And it's at the center of what your LH result is telling you.
What LH Actually Does
Think of LH as a text message from your brain to your testes. Your pituitary gland — a small structure at the base of your brain that acts as your hormonal control center — sends out pulses of LH throughout the day. Those pulses arrive at specialized cells in your testes called Leydig cells, which receive the signal and respond by producing testosterone.
That's LH's main job in men: telling your testes to make testosterone. Without that signal, the Leydig cells go quiet and testosterone production drops.
Here's where it gets interesting. The testosterone your testes make stays concentrated locally at levels around 50 to 100 times higher inside the testes than in your bloodstream. (PMC, 2022) That extraordinarily high local concentration is what sperm production actually requires. The testosterone level in your blood — what shows up on a standard test — is not the same as the testosterone level driving sperm production inside your testes. LH is what maintains that critical local environment.
This is why LH is in a fertility panel. It's not there because LH makes sperm directly. It's there because LH drives the testosterone production that makes sperm production possible — and your LH level tells you whether that system is working properly.
What a Normal LH Level Means
The reference range for LH in adult men is generally 1.5 to 9.3 mIU/mL, though this can vary slightly between labs. Within that range, the communication between your brain and your testes is functioning as it should: your pituitary is sending the right signal, your Leydig cells are responding, and testosterone is being produced at levels that support sperm development.
A normal LH alongside a normal testosterone and normal semen parameters is a reassuring set of results. It tells you the whole chain is working.
What High LH Means
When LH is elevated — above roughly 9.3 mIU/mL — it almost always means the same thing: your brain is sending a stronger signal because your testes aren't responding the way they should.
Here's the logic. When Leydig cells are damaged or underperforming, they produce less testosterone. Your brain detects the lower testosterone level and responds by increasing LH output — essentially turning up the volume to try to get more response. So high LH isn't the problem. It's your body's response to the problem, which is in the testes.
When high LH is combined with low testosterone, that's a particularly clear signal. It means your testes are being maximally told to produce testosterone and still can't keep up. This pattern — called primary hypogonadism — points toward conditions like Klinefelter syndrome, testicular damage from infection or injury, or other forms of primary testicular failure. (Merck Manual)
Research also shows that higher LH levels are associated with poorer sperm motility and morphology. (PMC, 2020) Not because LH harms sperm directly, but because elevated LH is the marker that Leydig cell function is compromised — and when Leydig cells aren't working well, the testosterone environment inside the testes that sperm need to develop in starts to break down.
What Low LH Means
Low LH — below about 1.5 mIU/mL — is a different problem with a different cause and, importantly, often a more treatable one.
When LH is low, the signal from the brain simply isn't reaching the testes adequately. Your Leydig cells may be perfectly healthy and capable of producing testosterone — they're just not being told to. The problem is upstream, in the brain's signaling system, not in the testes themselves.
The most common cause of low LH in men of reproductive age is taking external testosterone. When you take testosterone from outside the body — whether prescribed for low T or used for performance — your brain detects the elevated circulating levels and shuts down the HPG axis. LH drops to near zero. Your Leydig cells stop being stimulated. And crucially, the local testosterone concentration inside your testes collapses — even while your blood test shows normal or high testosterone from the external source. With no local testosterone signal, sperm production fails. This is why testosterone therapy has actually been studied as a male contraceptive. It is one of the most reliable ways to switch off sperm production. (PMC, 2022)
Obesity is another significant driver of low LH. Body fat — particularly belly fat — contains an enzyme that converts testosterone into estrogen. Higher body fat means more of this conversion, which means higher estrogen levels, which signals the brain to reduce LH. Lower LH means less Leydig cell stimulation, which means lower testosterone, which can lead to more fat gain. It's a cycle that starts with body composition and ends with impaired sperm production.
Other causes include pituitary adenomas (benign tumors that disrupt hormonal signaling), sleep apnea, chronic illness, and in some cases anabolic steroid use — which works through the same suppression mechanism as testosterone therapy.
The Testosterone Test Doesn't Tell the Full Story
This is the most practically important thing to understand about LH.
Many men are told their testosterone is "normal" and assume that means their fertility-relevant testosterone is also fine. But standard testosterone tests measure what's circulating in the bloodstream, serving your muscles, bones, brain, and other tissues. They don't measure the testosterone concentration inside the testes — where it needs to be at 50 to 100 times the blood level to support sperm production.
LH is what maintains that local concentration. A man with borderline-low LH may have a blood testosterone level that looks acceptable on a standard test, while the environment inside his testes is insufficient for normal sperm development. That gap is invisible without measuring LH alongside testosterone. (Male Infertility Guide)
This is also the core problem with testosterone replacement therapy for men who want to father children. The TRT brings blood testosterone up. It may even make a man feel better. But it suppresses LH to near zero, the Leydig cells stop working, and intratesticular testosterone collapses. The sperm production machinery shuts down — while the blood test looks perfectly normal.
Reading LH Alongside FSH and Testosterone
LH is most useful when read as part of a set. The combination of LH, FSH, and testosterone together tells a story that no single number can.
High LH with high FSH and low testosterone points to primary testicular failure. Both branches of the hormonal signaling system are being maxed out and the testes can't keep up. The problem is in the testes and is generally harder to treat.
Low LH with low FSH and low testosterone points to the signal from the brain being insufficient. The testes may be capable of working normally if properly stimulated. This pattern is more often treatable — through medications that restore the pituitary signal, or by addressing the underlying cause like testosterone use or obesity.
High LH with relatively normal FSH and low testosterone suggests Leydig cell dysfunction specifically — testosterone production is impaired while sperm production support may still be partially intact.
Normal LH with poor semen parameters means the signaling is working, but something else is going on downstream — which is why we look at the full picture rather than any single number.
What Can Be Done When LH Is Low
When the cause is exogenous testosterone, stopping it allows the HPG axis to recover. Recovery can take months and isn't guaranteed in all cases, particularly after long-term use. In men who need testosterone therapy but also want to preserve fertility, human chorionic gonadotropin (hCG) — an LH analog — can be given alongside testosterone to keep Leydig cells stimulated and maintain intratesticular testosterone. This requires clinical management and isn't a supplement-level intervention.
Clomiphene citrate, mentioned in the FSH article, raises LH and FSH together by blocking estrogen's feedback on the pituitary. It's used off-label in men with secondary hypogonadism and can restore both LH and testosterone in the right candidates.
For obesity-driven low LH, the most direct intervention is fat loss. Reducing body fat reduces estrogen conversion, which reduces estrogen-mediated suppression of LH, which allows the signal to recover. The entry point is metabolic, not hormonal.
Our Take
LH is the link between your brain's reproductive signal and the testosterone that sperm production actually depends on. When it's working properly, your Leydig cells are producing testosterone at the local concentrations your testes need. When it's too high, your brain is compensating for a problem in the testes. When it's too low, the signal isn't being sent — usually because something upstream is suppressing it.
The testosterone number in your bloodstream doesn't tell you whether your testes are getting the signal they need. LH does. That's why we measure it alongside FSH and testosterone as part of every SwimScore hormone panel — because understanding the full picture means knowing not just what your hormones look like, but whether the system producing them is working as it should.
This is Part 2 of the SwimScore Hormone Series. Next up: Testosterone — what your total and free levels actually mean for sperm production, and why TRT is one of the most common preventable causes of male infertility.
SwimScore uses CLIA-certified labs for all semen analysis and hormone testing, assessed against WHO 6th Edition clinical thresholds.
For more info on FSH, see part 1 here.
