Fertility Blood Tests for Men: Testosterone & FSH

Key Takeaways

Male factor infertility contributes to approximately 50% of couples struggling to conceive.
Blood tests should be taken in the morning (before 10am) when testosterone levels are at their peak.
FSH and LH help distinguish between problems with the testes and problems with the pituitary gland.
Blood tests complement semen analysis — both are usually needed for a full fertility assessment.

Why Blood Tests Matter for Male Fertility

When a couple is having difficulty conceiving, both partners should be investigated. Male factor infertility is a contributing cause in around half of all cases, yet it often receives less attention than female fertility testing. Hormonal blood tests provide critical information about whether the hypothalamic-pituitary-gonadal (HPG) axis — the hormonal system that controls sperm production — is functioning correctly.

NICE guidelines (CG156) recommend that men in couples who have been trying to conceive for 12 months without success should have a semen analysis as the first-line investigation. If the semen analysis is abnormal, or if there are clinical signs of a hormonal problem, blood tests are the next step.

Total Testosterone

Testosterone is the primary male sex hormone, essential for sperm production (spermatogenesis), libido, muscle mass, and bone density. The normal range in adult men is approximately 8.6–29.0 nmol/L, though ranges vary between laboratories. NICE and the British Society for Sexual Medicine suggest that levels below 8 nmol/L are clearly low, while levels between 8–12 nmol/L may warrant further investigation with free testosterone.

Testosterone levels follow a circadian rhythm, peaking in the early morning and declining throughout the day. For this reason, blood samples should always be taken before 10am for accurate results.

Free Testosterone

Most testosterone in the blood is bound to proteins — approximately 60–70% to sex hormone-binding globulin (SHBG) and 30–40% to albumin. Only 1–3% circulates as free (unbound) testosterone, which is the biologically active form. If total testosterone is borderline, measuring free testosterone or calculating it from total testosterone and SHBG levels can provide a clearer picture.

FSH (Follicle-Stimulating Hormone)

FSH is produced by the pituitary gland and stimulates the Sertoli cells in the testes to support sperm production. The normal range in men is approximately 1.5–12.4 IU/L.

Elevated FSH (above 12 IU/L) suggests primary testicular failure — the testes are not responding adequately, and the pituitary is producing extra FSH to try to compensate. This is often seen with severely impaired sperm production.
Low FSH suggests a pituitary or hypothalamic problem (hypogonadotropic hypogonadism), which may be treatable with hormone therapy.

LH (Luteinising Hormone)

LH stimulates the Leydig cells in the testes to produce testosterone. The normal range is approximately 1.7–8.6 IU/L. LH and FSH are interpreted together:

High LH + high FSH + low testosterone = primary hypogonadism (testicular problem).
Low LH + low FSH + low testosterone = secondary hypogonadism (pituitary/hypothalamic problem).
Normal LH + normal FSH + normal testosterone = the HPG axis is functioning normally; infertility may be due to other factors.

Prolactin

Prolactin is a pituitary hormone that, when elevated in men, can suppress GnRH (gonadotropin-releasing hormone) and consequently reduce testosterone and sperm production. The normal range is approximately 86–324 mIU/L. Elevated prolactin (hyperprolactinaemia) may be caused by a pituitary adenoma (prolactinoma), certain medications (particularly antipsychotics and some antidepressants), or hypothyroidism. Very high levels (above 5,000 mIU/L) strongly suggest a prolactinoma and require MRI imaging of the pituitary gland.

Oestradiol

Oestradiol (E2) is present in small amounts in men and plays a role in bone health and libido. Elevated oestradiol can suppress FSH and LH, impairing fertility. It may be raised in obesity (fat tissue converts testosterone to oestradiol via aromatase), liver disease, or with certain medications. The normal range in men is approximately 41–159 pmol/L.

Semen Analysis: The Essential Companion Test

Blood tests assess the hormonal environment, but they do not directly measure sperm quality. A semen analysis evaluates sperm count, motility (movement), and morphology (shape). WHO 2021 reference values include a total sperm count of at least 39 million per ejaculate and at least 42% progressive motility. Two abnormal semen analyses, taken 3 months apart, are needed before a diagnosis of male factor infertility is made.

Age-Related Changes

Unlike female fertility, which has a clear age-related decline, male fertility decreases more gradually. Testosterone levels decline by approximately 1–2% per year after the age of 30. Sperm quality also diminishes with age, with increased DNA fragmentation and a slightly higher risk of genetic abnormalities in offspring. However, men can remain fertile well into their later years, and age alone does not necessarily indicate a problem.

Getting Tested at Home

Fertility blood tests for men need to be taken early in the morning for accurate testosterone results. A mobile phlebotomist can visit your home before 10am to take the required blood samples, making it easy to get tested at the optimal time without needing to travel. Visit our home blood test page to book a male fertility hormone panel.