The level in blood serum differs widely between males and females, so it was easy to set a cut-off between the two. In a female, any level above 1.7 nanomoles per litre (nmol/L) suggests the presence of testicular material or a tumour, whereas 7.7 nmol/L is right at the bottom of normal for an elderly man. The authorities settled on 10 nmol/L, much lower than healthy males in their prime, to be maintained for a year before a transwoman could compete as a woman.
