A female athlete with hyperandrogenism who has testosterone levels in the male range (as measured by a blood test) will not be eligible to compete as a woman. The IOC has not yet decided on the cut-off levels, but the normal range of total testosterone for an adult premenopausal women is typically defined as 15-70 nanograms per deciliter, compared with 260-1,000 nanograms per deciliter for a man.
There are exceptions, though. The most common cause of extreme hyperandrogenism is androgen insensitivity syndrome (AIS). In these cases, an embryo is genetically male but lacks a fully functioning receptor for testosterone, so does not respond normally to the hormonal signal to become male. In typical cases, she develops as a female -- although with internal testes instead of ovaries. The IOC and IAAF concluded that, because such women are resistant to androgens, they gain no competitive advantage from their high testosterone levels and have exempted them from the ban.
"If you have AIS, you should still be able to compete," says Malcolm Collins, a medical biochemist specializing in sports medicine at the University of Cape Town, who was not involved in drawing up the guidelines.
Women with testosterone levels that are high but below the male range - as commonly occurs with conditions such as polycystic ovary syndrome - would also be unaffected by the ban.
The IOC says that an athlete banned from female competition under these regulations would not be eligible to compete as a male