So a pure-blood could only be a female? Daughter of Coldharbour and all that. =/
Nope, males can be too.
Don't trust the wiki's. Many people add stupid stuff. "Daughters of Coldharbour" is a confluence given to females that become pureblooded vampires. I suppose males get another alternate way of becoming pureblooded, like offering souls to Molag Bal as sacrifices. Harkon himself did it and was pureblooded. Perhaps they are called "Sons of Coldharbour"?
In any case, it is extremely rare and it happens to vampires who truly know what they're dealing with.