The testicles produce most of the body's supply of male hormones. These hormones are called androgens and the most important of the androgens is a hormone called testosterone.

Treatment for a testicular cancer usually involves an operation to remove the affected testicle (this type of surgery is called an orchidectomy). This may then be followed by chemotherapy or radiotherapy.

Normally removing just one testicle doesn't cause any problems with testosterone levels in the blood, the remaining testis is able to produce enough of the hormone. Occasionally though the remaining testicle may not be functioning properly or sometimes both testicles may be affected by a cancer and both may have to be removed, in these situations testosterone deficiency can develop in the months after surgery.

It is possible to do a blood test to measure the concentration of testosterone in the blood. The concentration of the hormone is measured in nanomoles per litre (which is shortened to 'nmol/L'). The normal range of testosterone levels is from 10nmol/L up to 41nmol/L, in healthy young men.

If the blood test shows a level of testosterone much less than 10nmol/L then symptoms of male hormone deficiency are quite likely (with tiredness, weakness, low mood and depression and loss of sexual interest and libido). In this situation male hormone replacement therapy (HRT) is often worthwhile.

Some men who have had treatment for testicular cancer will have testosterone blood levels within the normal range (but towards the lower end of that range) and still have some symptoms of male hormone deficiency. If this happens doctors will often do a second type of blood test measuring another hormone called luteinising hormone (LH). LH is produced by the pituitary gland, at the base of the brain, and this controls the production of testosterone by the testicles. If testosterone levels become low then LH levels in the blood will increase. So if a blood test shows an abnormally high level of LH and a level of testosterone that is towards the lower end of the normal range, then these findings will usually lead doctors to decide that there is a deficiency and that a trial of HRT might help.