This case-sensitive code system http://hl7.org/fhir/us/cdmh/CodeSystem/pcornet-death-cause-codes defines the following codes:

Code	Display	Definition
09	ICD-9	Death Cause values are from ICD-9
10	ICD-10	Death Cause values are from ICD-10.
NI	No information	Death Cause value has No information.
UN	Unknown	Death Cause value is Unknown.
OT	Other	Death Cause value is Other.