# CDSS Request A CDSS request technically corresponds to a referral of the patient to the CDSS. For this purpose, the FHIR Resource {{link:EviPrevIt/eviprevReferralRequest}} is transmitted. The observations with the measurement data must be stored under supportingInfo. The workflow of a referral can be asynchronous or synchronous. Only synchronous transfer is supported by EviPrev. The EviPrev CDSS performs the desired calculations and returns a {{link:EviPrevIt/eviprevDiagnosticReport}}. For each rule, an observation with the result is delivered under "result". If no result could be determined for a given rule, e.g. because a parameter is missing, this will be coded in the corresponding observation under "dataAbsentReason". {{tree:EviPrevIt/cdssRequest}} *** {{pagelink:EviPrevIt/CDSSRequestInput}} ยป