Combo Box data

I have a combo box that has a three field query, the bound field is field 1, Because field 1 is a concatanated field (Last Name, First Name) I use that to look up the user information. However if there are two persons with the same last and first name I want to use the birthdate as the next lookup. Is there anyway in VBA to find that third column in my combo box query?
Thanks for any help.