Women

LH is most often used in the investigation of menstrual cycle irregularities, such as oligomenorrhoea/amenorrhoea, as part of infertility investigations and to further evaluate disorders of the pituitary gland. LH should be interpreted alongside FSH to determine a more focused clinical picture. While many women with PCOS can still have FSH and LH levels within the acceptable range, the LH level is typically found to be two or three times that of the FSH level, also referred to as elevated LH to FSH ratio. This change is enough to disrupt ovulation. This used to be considered an important aspect in diagnosing PCOS, it is now considered less useful in diagnosing PCOS, but is still helpful when looking at the overall picture in conjunction with clinical presentation and imaging results. Low levels of LH in conjunction with low FSH and low GnRH and indicate a disruption of the hypothalamic pituitary ovarian axis – hypogonadotrophic hypopituitarism. This is a reversible condition often caused by excessive weight loss, exercise or stress.  In children with sexual characteristics, high levels FSH and LH indicate the onset of precocious puberty, a condition more common in girls.

Males

In men, LH stimulates androgen synthesis by acting on the interstitial Leydig cells of the testes, stimulating them to produce testosterone and dihydrotestosterone. Primary hypogonadism, or hypergonadotrophic hypogonadism is caused by testicular failure and is characterised by low serum testosterone and high FSH & LH concentrations. It results from testicular injury, after mumps infection, alcohol abuse, post chemotherapy and radiation treatment or as a result of genetic defects which affect testicular development, ie Klinefelter syndrome. In secondary hypogonadism, hypogonadotrophic hypogonadism occurs due to a defect in the hypothalmus or pituitary. This results in low LH & FSH levels which impair testicular function because of the insufficient stimulation of the Leydig cells. This can be reversed with appropriate hormonal treatment whereas those with primary hypogonadism resulting from testicular failure cannot.