As of 2015, blood tests before marriage are only required in the District of Columbia, Mississippi and Montana, according to Nolo. Blood tests were once mandatory before marriage across the United States, but many states no longer require them.
The state of Montana only requires blood tests before marriage for females. The state of New York requires sickle cell testing from Hispanic and African-American applicants. In the states where a blood test is required, the clerk cannot issue a marriage certificate until the parties provide the results of a recent blood test. The main purpose of the test is to check for venereal diseases.