DNA testing cannot prove that people are Native American. There are no unique genes for tribes or Native Americans as a whole. There are some genetic markers that are found mostly only in Native Americans and Alaska Natives, but they are not unique to the races.
Primarily, DNA testing can be used to establish paternity or ancestral relationships between two people. Typically, DNA testing is most accurate when comparing individuals in the same direct lineage, such as children to their parents, siblings and grandparents. It is less effective when comparisons are made in extended family relationships.
Traditionally, Native American ancestry and tribal role memberships have been decided by the blood-quantum method. This method traces ancestral family trees to decide what percentage of Native American or Alaska American blood is in a specific person, and from which tribe. A person's blood quantum is calculated as a percentage of lineage. If an individual's father is one-half Native American, but his mother is not, then the person is considered to be one-quarter Native American. This quantum is recorded on the person's Certificate Degree of Indian or Alaska Native Blood card. Historically, the U.S. Bureau of Indian Affairs used the blood-quantum method to decide who would be considered Indian and who would not.