This case-insensitive code system https://www.ehealth.fgov.be/standards/fhir/core-clinical/CodeSystem/be-cs-problem-origin-type defines the following codes:

Code	Display	Definition
referral	Referral order	Following a referral order
own-initiative	Patient's own initiative	The patient has arrived on their own initiative
counsel	Advice or recommendation from another provider (no prescription)	From an advice or recommendation of a health professional (without prescription)
other	other	Other

Additional Language Displays

Code	French (Belgium) (fr)	Nederlands (België) (Dutch (Belgium), nl)
referral	prescription de renvoi	verwijsvoorschrift
own-initiative	libre	Op eigen initiatief
counsel	conseil	doorverwijzing
other	autre	andere