That may seem like a mere technical ruling. The female range for testosterone is categorically different from the male range. In general, males have 10 to 30 times more T than females. Most females, including most elite female athletes, have T levels in the range of 0. The reason there is a gap, with no overlap between the ranges, is that beginning in puberty, the testes produce a lot more T than ovaries and adrenal glands combined. No single tool is perfect for these purposes, but testosterone comes pretty close. Sport already tests for T levels as part of standard anti-doping controls, and it is much less intrusive than other diagnostic techniques used to determine sex.