FSH and LH Blood Tests

What are FSH and LH?

FSH (follicle-stimulating hormone) and LH (luteinising hormone) are gonadotropins produced by the pituitary gland. In women, FSH stimulates ovarian follicle development and oestrogen production; LH triggers ovulation. In men, FSH stimulates sperm production (spermatogenesis) in the testes; LH stimulates testosterone production from Leydig cells. These hormones are part of the hypothalamic-pituitary-gonadal (HPG) axis and are used to evaluate fertility, menopause and pituitary problems.

FSH and LH normal ranges

What does HIGH FSH mean in women?

What does HIGH LH in women mean?

What do LOW FSH and LH mean?

What do HIGH FSH and LH mean in men?

Questions to ask your doctor

• Should I test on day 2 or day 3 of my cycle?
• Do I need an AMH (anti-Mullerian hormone) test to check my egg reserve?
• What is my FSH:LH ratio?
• Does this result mean I am in menopause?
• Should I see a fertility specialist or endocrinologist?

References

The clinical information on this page is drawn from peer-reviewed sources indexed by the US National Library of Medicine. Links go to the source so you can read it yourself.

1. Physiology, Anterior Pituitary. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK499898

References

Sources cited on this page. PubMed links open the original abstract.

1. Balen AH, Morley LC, Misso M, et al. The management of anovulatory infertility in women with polycystic ovary syndrome. Hum Reprod Update. 2016;22(6):687–708. PMID 22781167 · doi:10.1093/humupd/dmw025

How the FSH/LH ratio helps diagnose the cause of infertility

Follicle-stimulating hormone (FSH) and luteinising hormone (LH) are glycoprotein hormones produced by the pituitary gland. They work in concert to regulate ovarian and testicular function, and interpreting them together – rather than in isolation – provides far more diagnostic power.

In women, a raised FSH with a raised LH in the context of absent periods typically indicates primary ovarian insufficiency (POI, previously called premature ovarian failure) – the ovaries are not responding to pituitary signals. By contrast, a low FSH and low LH points to hypothalamic or pituitary dysfunction (secondary hypogonadism), which has a very different cause and treatment pathway. In polycystic ovary syndrome (PCOS), the LH:FSH ratio is classically greater than 2:1, though this criterion is no longer required for diagnosis under the Rotterdam criteria.

The FSH surge and ovulation detection

In the normal menstrual cycle, FSH rises gradually in the early follicular phase to stimulate follicle development, then a sharp mid-cycle LH surge (and smaller FSH co-surge) triggers ovulation approximately 36 hours later. Home ovulation predictor kits measure this LH surge in urine. Timed blood tests to confirm ovulation typically measure a post-ovulatory progesterone level on day 21 of a 28-day cycle rather than LH or FSH, since the LH surge is very brief.

Male FSH and LH testing in azoospermia

In men presenting with azoospermia (no sperm in the ejaculate), FSH and LH are critical for distinguishing obstructive azoospermia from non-obstructive (testicular) azoospermia. Elevated FSH with elevated LH in an azoospermic man suggests testicular failure (Sertoli-cell only syndrome, maturation arrest) – the testes are not producing sperm despite maximal pituitary stimulation. Normal FSH and LH with azoospermia suggests a mechanical obstruction (e.g., vasectomy, blocked vas deferens or epididymis) where sperm production is occurring but cannot exit – surgical reconstruction or sperm retrieval may be possible. LH levels also help assess testosterone production: low LH with low testosterone suggests a pituitary or hypothalamic cause rather than primary testicular failure.