Every test, explained.

LH, in full luteinising hormone, is the hormone from your pituitary that in women gives the starting signal for ovulation and in men sets the testes to making testosterone. In women not one normal value but a range per cycle phase, with a surge around ovulation a multiple higher than the rest.

FSH, in full follicle-stimulating hormone, is the signal with which your brain sets the ovaries or the testes to work: low when they respond well, high when they respond less, and permanently high after the menopause. In women not one normal value but a range per cycle phase.

Prolactin is the hormone from your pituitary that starts milk production after childbirth and outside that time acts as a brake on your sex hormones: a raised value suppresses LH and FSH, and with them the cycle, desire and testosterone. Have blood drawn in the morning, rested and without exercise or sex beforehand, and read it beside LH, FSH and TSH.

Total testosterone adds up all the testosterone in your blood, the part bound to protein and the free part together. It is the hormone that carries muscle, bone, desire and energy, and one of the hormones that move most with how you live. Have blood drawn before ten in the morning, and read it beside SHBG, which decides how much of it works.

SHBG, in full sex hormone binding globulin, is the protein from your liver that holds testosterone and oestradiol in your blood and so decides how much of them stays active. It is also one of the first values to give away insulin resistance. Read it beside total testosterone and have the free share calculated.

Free testosterone is the part of your testosterone not bound to protein and therefore able to do its work, calculated from your total testosterone, your SHBG and your albumin. It is the number that fits complaints best when SHBG is abnormal.

The free androgen index is a calculation: your total testosterone divided by your SHBG, the protein that binds testosterone. The result estimates how much of your testosterone is free and therefore works, and is above all in women with excess hair growth, acne or an irregular cycle a more usable number than the total alone.

Oestradiol is the main oestrogen: in women the hormone that carries the first half of the cycle and keeps bone, vessels and mucous membranes healthy, in men a small amount that arises from testosterone. A regular cycle with ovulation is the health signal, and eating too little, training too much and stress are what switch it off.