In a policy memorandum dated October 17, 2014, United States Citizen and Immigration Services stated that they will not accept DNA test results to prove a sibling relationship.  This decision was based on the fact that the test is not reliable.  The Service stated that “the DNA testing industry has not established probability standards for sibling-to-sibling DNA test results.”  The Service, however, will still continue to accept DNA test results to establish the parent-child relationship.

Source: USCIS Policy Memorandum