This case-sensitive code system http://hl7.org/fhir/us/directory-query/CodeSystem/CredentialStatusCS defines the following codes:

Code	Display	Definition
active	active	The credential may be considered valid for use.
inactive	inactive	The credential may not be considered valid for use.
issued-in-error	issued in error	The credential was mistakenly assigned and should not be considered valid for use.
revoked	revoked	The credential was revoked by the issuing organization and should not be considered valid for use.
pending	pending	The credential has not been officially assigned. It may or may not be considered valid for use.
unknown	unknown	The status of this credential is unknown. It may or may not be considered valid for use.