The bound value set for USCoreRace (ValueSet Omb Race Category) includes two values from the NullFlavor codesystem which allows for the indication of an "unknown" (UNK) or "asked but unknown" (ASKU) value in addition to the five OMB Race categories.

We propose adding these NullFlavor values to the existing ethnicity codes in ValueSet Omb Ethnicity Category to allow for the expression of missing and/or declined responses for USCoreEthnicity, as it is done in USCoreRace.