Why it is for you

The root-cause picture is a reproductive axis that has gone quiet from above rather than failed at the gland. That is low testosterone with low or normal LH rather than high LH, a cycle that stopped under heavy training or low body fat, desire that went before anything else did, or puberty that never arrived. The question it answers better than any other molecule is diagnostic: ask the hypothalamus, and if the pituitary answers, the machinery is intact and the fault is in the signalling above it. It pairs with the metabolic work that caused the problem in the first place, since fuel state reaches reproduction through this exact node, so weight, training load and sleep are part of the same answer. It is the wrong tool where the testis or ovary itself has failed, because there is nothing downstream left to shout at. The work of giving it, and of measuring what answers, belongs with a clinician.