LH and FSH are two hormones from your pituitary that drive your testicles. LH switches on testosterone production, FSH helps drive your sperm production. That is exactly why they are so telling: with a low testosterone, LH and FSH reveal whether the problem sits in your brain or your testicles. That single distinction often decides which next step makes sense.
I often see men look only at testosterone. But without LH and FSH you do not know where a low number comes from.
What are LH and FSH?
LH (luteinising hormone) and FSH (follicle-stimulating hormone) come from your pituitary, a small gland in your brain. LH prompts the Leydig cells in your testicles to make testosterone. FSH acts on the Sertoli cells and, together with testosterone, drives your sperm production.
Together your brain, pituitary and testicles form a feedback system. If your testosterone drops, your pituitary is meant to notice and release more LH.
What is a normal LH and FSH value in men?
In adult men LH sits broadly between about 1.5 and 9.3 IU/L and FSH between about 1.4 and 18.1 IU/L, though the reference range varies by lab. The numbers themselves matter less than their combination with your testosterone.
| Pattern (with low testosterone) | What it may sometimes suggest | What your doctor often checks alongside |
|---|---|---|
| Low testosterone with high LH and FSH | The testicles respond poorly (primary hypogonadism) | Testicular assessment, sometimes genetic testing |
| Low testosterone with low or normal LH and FSH | The drive from the brain falls back (secondary) | Prolactin, iron, weight, medication, pituitary |
| Normal testosterone with normal LH and FSH | The axis is in balance | Usually no further action |
What does a high LH and FSH mean?
A low testosterone with a high LH and FSH points to primary hypogonadism: your brain calls louder, but your testicles deliver too little (Karakas, 2018). Causes range from earlier testicular damage to congenital conditions. A high FSH with small testicles can also point to reduced fertility.
With this pattern the key sits in the testicles, not the brain.
What does a low or normal LH mean with a low testosterone?
A low testosterone with a low or normal LH and FSH points more to secondary hypogonadism: the signal from your brain falls back. This often fits with excess weight, long-term stress, opioid use, a raised prolactin or a pituitary problem. Because this is often reversible, it pays to look for the cause.
What do LH and FSH mean for your fertility?
FSH is the hormone most closely tied to fertility. It drives the Sertoli cells, which support sperm production. A raised FSH with small testicles can point to reduced sperm production, even if your testosterone is still reasonable.
LH is linked to fertility indirectly, through testosterone that is needed locally in the testicle for sperm to mature. Still, only a semen analysis gives a clear answer on your fertility; LH and FSH mainly give context.
Picture a couple who have been trying to conceive for a year. In the man, FSH is raised and the testicles are somewhat small. That shifts attention to testicular function, and a semen analysis is then the logical next step to discuss with the GP.
So LH and FSH help narrow the question, without setting a diagnosis on their own.
What does the LH/FSH ratio say?
The ratio between LH and FSH gives extra context, especially around fertility. A selectively raised FSH can point to a problem with sperm production, while testosterone and LH still look reasonable. Even so, the pattern of both hormones together with your testosterone leads, not a single number.
Reliable Dutch-language patient information on hormone complaints and fertility is maintained by GPs at Thuisarts.nl.
How do you get LH and FSH measured?
LH and FSH are best drawn in the morning, together with your testosterone and SHBG, because they only read well together (Harman et al., 2001). Because free testosterone is calculated from testosterone and SHBG (Narinx et al., 2022), that usually belongs with it. The LH value and FSH value sit together on the Hormones Man test.
So always read LH and FSH next to your testosterone. The overview is in male sex hormones, and the wider context in the pillar on male hormonal health. If you see an abnormal pattern, discuss it with your GP.
Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
Sources
- Karakas SE. New biomarkers to evaluate hyperandrogenemic women and hypogonadal men. Adv Clin Chem. 2018. PMID 30144842.
- Harman SM, et al. Longitudinal effects of aging on serum total and free testosterone levels in healthy men. J Clin Endocrinol Metab. 2001. PMID 11158037.
- Narinx N, et al. Role of sex hormone-binding globulin in the free hormone hypothesis and the relevance of free testosterone. Cell Mol Life Sci. 2022. PMID 36205798.
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