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

Code	Display	Definition
OD	Internal administration	Source of the information is Internal administration.
EF	External feed	Source of the information is External feed.
IS	Immunization Information Systems	Source of the information is Immunization Information Systems.
PR	Patient-reported	Source of the information is Patient-reported.
PD	Patient Device Direct Feed	Source of the information is a Patient Device Direct Feed.
HC	Healthcare	Source of the information is Healthcare organization such as problem list.
HD	Healthcare Device Direct Feed	Source of the information is Healthcare Device Direct Feed.
RG	Registry cohort	Source of the information is Healthcare organization such as problem list.
CC	Patients Cheif Complaint	Source of the information is Patients Chief Complaint
PC	PCORNet condition algorithm	Source of the information is PCORNet defined condition algorithm
DR	Derived	Source of the information is Derived.
NI	No information	There is No Information on the source of the data.
UN	Unknown	Source of the information is Unknown.
OT	Other	Source of the information is Other.