Male Fertility Blood Test: The Hormones Behind Sperm Production

1. How hormones drive sperm production

Sperm production runs on a feedback loop between the brain and the testicles, the hypothalamic-pituitary-gonadal (HPG) axis. The pituitary gland releases two gonadotrophins: luteinising hormone (LH) and follicle-stimulating hormone (FSH).

LH tells the Leydig cells in the testes to make testosterone. FSH, together with that locally produced testosterone, drives the Sertoli cells that physically support sperm development. As one review of the endocrine control of spermatogenesis puts it, FSH is required to set the number of Sertoli cells and to initiate and maintain normal sperm production. The testosterone inside the testicle (intratesticular testosterone) sits at concentrations many times higher than in your blood — and that local concentration, not your blood level, is what spermatogenesis actually needs.

This is the single most important idea in this guide, and the one most men get wrong: a “normal” blood testosterone does not guarantee healthy sperm production, and topping up blood testosterone with medication can switch sperm production off entirely. We come back to that in the section on TRT.

2. Blood test vs semen analysis: what each one measures

A male fertility investigation has two halves, and they answer different questions.

A semen analysisis the direct measurement of the sperm themselves — count, concentration, motility (how well they move) and morphology (shape). It is the first-line test and the only one that tells you about the sperm in front of you. The WHO 2021 (sixth edition) lower reference limits are a sperm concentration of 16 million per millilitre, total motility of 42%, and 4% normal forms. A semen analysis cannot be done from a finger-prick — it needs a fresh semen sample analysed in a lab.

A fertility hormone blood test measures the machinery upstream of the sperm: testosterone, LH, FSH and prolactin. It cannot tell you your sperm count. What it can do is explain whya count might be low, and point to whether the problem sits in the brain (pituitary) or the testicles — which changes what a specialist does next.

NICE NG257 reflects exactly this order of operations: semen analysis first, and for men with two or more abnormal semen analyses, serum testosterone and gonadotrophin (LH and FSH) levels should be considered. The blood test is the explainer, not the diagnosis.

3. The four markers that matter (and two that help)

Two more add useful context. SHBG and a calculated free testosterone show how much of your testosterone is actually available rather than bound up, and DHEA-S reflects the adrenal contribution to your androgen pool. Our Complete Male Hormones panel measures all six — testosterone, free testosterone, SHBG, LH, FSH and prolactin — plus DHEA-S and albumin, from a finger-prick at home.

4. What your result pattern means

The combination of LH, FSH and testosterone — read together, never in isolation — localises where the problem sits. These patterns are drawn from the differential diagnosis of azoospermia and are for understanding only — a qualified clinician must interpret your actual results.

Notice that the most useful information often comes from the markers being read against each other. A testosterone of 11 nmol/L means something very different with a low LH than with a high one.

5. The TRT and anabolic steroid trap

This is the single most preventable cause of male subfertility, and it catches men who think they are doing the right thing.

When you take testosterone from outside the body — whether prescribed testosterone replacement therapy or anabolic steroids — your brain senses plenty of testosterone and stops sending the LH and FSH signals. Without those signals, intratesticular testosterone collapses and sperm production can shut down, sometimes to the point of zero sperm in the ejaculate (azoospermia). Exogenous testosterone is, in effect, a male contraceptive.

The good news is that it is usually reversible. In recovery studies, 64–84% of men regained sperm production after stopping, with a median of around 110 days — though for some it took up to two years. This is why NICE is explicit that androgens should not be used to treat sperm abnormalities, and why any man on testosterone who wants to conceive needs a specialist conversation, not a higher dose.

A telling blood-test fingerprint of exogenous testosterone use is a normal or high testosterone sitting next to a suppressed (very low) LH and FSH — the mirror image of natural production.

6. What a blood test won't catch

A hormone panel is one lens, not the whole picture. Several common causes of male subfertility on the NHS list produce normal hormones:

• Varicocele— enlarged veins in the scrotum, found in a meaningful share of subfertile men, often with normal hormones.
• Obstruction— a physical blockage from infection, surgery (including vasectomy) or a congenital absence of the tubes.
• Sperm quality issues— poor motility or morphology that only a semen analysis reveals.
• Ejaculatory problems— including retrograde ejaculation, which a hormone test will not detect.

This is exactly why the blood test complements, rather than replaces, a semen analysis and a clinical examination. If you are early in the process, our fertility blood test guide for couples sets the female and male sides side by side.

7. When and how to test (timing matters)

Testosterone follows a daily rhythm, peaking in the morning, so the timing of the sample changes the number you get. The BSSM guidance is to measure testosterone from a fasting morning sample, ideally before 10am, and to confirm any low result with a repeat. Our guide to the best time to test testosterone has the full checklist.

LH, FSH and prolactin are also best measured in the morning. A useful first panel includes total testosterone, free testosterone (calculated from SHBG), LH, FSH and prolactin together — because, as section 4 showed, the value is in reading them as a set.

One practical note on prolactin: it rises with stress, sleep disruption and even a difficult blood draw, so a single mildly raised result is usually repeated, rested and relaxed, before anyone acts on it.

8. What you can actually change

Sperm take around three months to develop, so changes you make today show up in a semen analysis roughly a quarter of a year later. The evidence-backed levers are unglamorous but real:

• Stop exogenous testosterone and steroidsif fertility is the goal (see section 5) — the highest-impact change for anyone affected.
• Reach a healthier body composition. Excess body fat raises oestrogen and lowers testosterone, and is linked to poorer semen parameters.
• Cut heat, smoking and heavy alcohol. Frequent saunas, hot baths and laptops on the lap all warm the testicles; smoking and heavy drinking both lower sperm quality.
• Correct documented nutrient deficiencies.Zinc contributes to normal fertility and reproduction and to the maintenance of normal blood testosterone — both authorised GB nutrition and health claims for the nutrient zinc — but the benefit is in correcting a real shortfall, not loading up regardless. Our zinc guide covers how to measure it.

What does notwork is buying an over-the-counter “fertility booster” without knowing your numbers. Measure first, then act on what the result actually shows.

9. The UK pathway

1. Semen analysis first. NICE advises a couple who have not conceived after a year of regular unprotected sex (or sooner if there is a known reason) to be investigated, starting with a semen analysis for the man.
2. Repeat if abnormal.An abnormal first result is repeated to confirm — single readings are not relied on.
3. Hormone bloods next. For two or more abnormal semen analyses, NICE NG257 says serum testosterone and gonadotrophins (LH, FSH) should be considered, which is where the patterns in section 4 come in.
4. Specialist referral. A urologist or fertility specialist examines the scrotum and decides on next steps. For hypogonadotropic hypogonadism, gonadotrophin therapy can be offered to restore fertility.

Many men test privately to arrive at that appointment with correctly-timed hormone results already in hand — not to self-treat, but to make the consultation faster and more informed.

Frequently asked questions