Well, those with CAIS can't be female. By definition. Even though you'd never know it without doing their karyotype, or giving them an X-ray.

CAIS = Complete Androgen Insensitivity Syndrome. Males whose bodies don't respond at all to masculinizing hormones (like testosterone) develop, from the time they're in utero, to appear female. But the key word is appear. Internally, their gonads are male-- instead of a uterus and ovaries, they have testes-- and their chromosomes are XY.