United States citizens can petition for their spouses, parents, children or siblings to immigrate to the United States and permanent residents can do so for their spouses and unmarried children.
In most cases there are sufficient written records to validate relationships and satisfy the requirements of the U.S. Citizen and Immigration Services Department. If more evidence of a biological relationship is needed, a voluntary DNA test may be advised. Tests are typically requested for immigration and passports and sometimes for other reasons. It is important to ask the reason for testing, as that could dictate which U.S. agency is responsible for sample collection and receiving reports.