Male factors contribute to nearly half of all infertility cases. Yet in most couples, the investigation begins and sometimes ends with the woman. Testosterone, FSH, LH, prolactin, thyroid function, and metabolic health all directly affect sperm production and quality. A comprehensive blood test like the TrueVitals Ultimate panel checks every hormonal, metabolic, and nutritional marker that influences male fertility across 114 biomarkers. Get tested at the same time as your partner, not 12 months later.
The WHO estimates that infertility affects approximately 15 to 20% of couples worldwide, with male factors contributing to nearly half. A cross-sectional study published in 2025 found that hormonal imbalances, specifically low testosterone and elevated prolactin, were significantly associated with abnormal semen profiles. Yet male fertility investigation is often an afterthought. In many couples, months of tests and interventions are directed at the woman before anyone suggests the man should be checked.
The NHS pathway reflects this. NICE recommends offering a semen analysis within the first year of investigation, but the initial GP conversation almost always centres on the woman's cycle, ovulation, and hormones. The man is offered a semen analysis — and if that comes back "normal," the investigation of the male partner typically ends. Hormonal blood work for the man is usually only requested if the semen analysis shows a count below 5 million/mL.
The problem is that hormonal imbalances can impair sperm quality (motility, morphology, DNA fragmentation) even when the count is within range. A man with a count of 20 million but low testosterone, elevated prolactin, and subclinical hypothyroidism may have a "normal" semen analysis by WHO criteria while his hormonal environment is actively undermining fertility. Blood testing identifies the cause. Semen analysis measures the consequence. Both are needed.
Sperm production is driven by a hormonal cascade from the brain to the testes. A disruption at any point in the chain reduces output. Blood testing reveals exactly where the chain is breaking.
The hypothalamus releases GnRH, which tells the pituitary gland to release LH (luteinising hormone) and FSH (follicle-stimulating hormone). LH stimulates the testes to produce testosterone. FSH drives Sertoli cells to support sperm development. If LH and FSH are low, the brain isn't signalling the testes properly (secondary hypogonadism). If they're elevated, the testes aren't responding (primary hypogonadism). This distinction is critical because the treatments are different.
Testosterone is essential for spermatogenesis. Low testosterone (below approximately 12 nmol/L) impairs sperm production. But free testosterone matters as much as total — high SHBG binds testosterone and reduces the amount available for biological activity. Testing both total testosterone and SHBG (with free testosterone calculated) reveals the true hormonal picture. Testosterone blood test guide.
Elevated prolactin suppresses GnRH, which suppresses LH and FSH, which suppresses testosterone and sperm production. Significantly elevated prolactin (above 30 mcg/L) can cause erectile dysfunction, low libido, and gynecomastia. Causes include prolactinoma (a benign pituitary tumour, more common than most people realise), certain medications, hypothyroidism, and chronic stress. It is treatable, often dramatically, with cabergoline. But it must be tested to be found. ED and prolactin guide.
Testosterone converts to oestradiol via the enzyme aromatase, concentrated in abdominal fat. Men carrying excess abdominal weight produce more oestradiol, which feeds back to suppress GnRH and further reduce testosterone. High oestradiol relative to testosterone is a common and correctable hormonal pattern in men with fertility concerns, particularly those who are overweight.
Both hypothyroidism and hyperthyroidism impair male fertility. Low thyroid function reduces sperm motility and increases DNA fragmentation. The connection is underappreciated in male fertility — thyroid testing is standard for women trying to conceive but rarely offered to men. Full thyroid (TSH, Free T4, Free T3) should be part of every male fertility panel. Thyroid blood test guide.
This is the most important paragraph on this page. Exogenous testosterone (TRT, anabolic steroids, testosterone boosters containing actual testosterone) suppresses FSH and LH. When the pituitary detects high circulating testosterone, it stops signalling the testes to produce more. FSH drops. Spermatogenesis slows or stops entirely. Some men on TRT become effectively azoospermic (zero sperm).
If blood work shows low testosterone AND you are trying to conceive, a fertility specialist may prescribe alternatives that boost testosterone without suppressing spermatogenesis: clomiphene citrate (off-label but widely used), hCG (human chorionic gonadotropin), or aromatase inhibitors. These maintain or improve the hormonal environment for sperm production while raising testosterone. Starting TRT in this situation could make conception impossible until it's discontinued, and recovery of spermatogenesis after stopping TRT takes months and is not guaranteed.
Get the blood test before making any hormonal decision. The data changes everything. Blood test before TRT guide.
Insulin resistance impairs testosterone production and is associated with reduced sperm quality. Abdominal obesity increases aromatisation. Metabolic health is directly linked to reproductive health.
Vitamin D receptors are present in testicular tissue. Deficiency is associated with reduced sperm motility. Most UK men are deficient in winter. Target 75 to 125 nmol/L.
Zinc is essential for testosterone production and sperm development. Selenium protects sperm from oxidative damage. Both are commonly suboptimal in UK diets and correctable with supplementation.
Folate is not just for women. Male folate deficiency is associated with increased sperm DNA damage. B12 supports sperm count and motility. Both are testable and correctable.
Chronic stress elevates cortisol, which suppresses the HPG axis and reduces testosterone. Stress is not a minor factor — it has a measurable biochemical impact on the hormonal chain that produces sperm. Stress blood test guide.
Cholesterol is the precursor molecule for all steroid hormones, including testosterone. Extremely low cholesterol can impair testosterone synthesis. Elevated cholesterol affects cardiovascular and metabolic health. Balance matters.
The TrueVitals Ultimate panel covers total and free testosterone, SHBG, FSH, LH, prolactin, oestradiol, full thyroid, cortisol, fasting insulin, HOMA-IR, vitamin D, B12, folate, ferritin, zinc, and 100+ additional markers. 114 biomarkers. Results in 48 hours. £349.
A full sperm production cycle takes approximately 74 days from stem cell to mature sperm. This means any intervention you make today — correcting a thyroid problem, addressing insulin resistance, supplementing zinc, treating elevated prolactin — takes at least 3 months to show up in a semen analysis. The hormonal environment you create now determines the sperm quality 3 months from now.
This is why testing early matters. If you wait 6 months before investigating your hormones, any correctable issue you find will take another 3 months to improve. That's 9 months of delay for a problem that could have been identified and addressed in the first week.
The recommended approach: both partners test at the same time, as early as possible. Man gets a comprehensive blood test plus a semen analysis. Woman gets a comprehensive blood test with fertility markers. If issues are found, intervene immediately. Retest hormones at 6 to 8 weeks (to confirm the intervention is working) and semen analysis at 3 months (to see the downstream effect). Every month of earlier testing is a month of earlier intervention.
114 biomarkers covering every hormonal, metabolic, thyroid, and nutritional marker that affects male fertility. Get tested at the same time as your partner. Results in 48 hours. £349.
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