Hi,
It is sometimes undesirable to send a full demographic or results feed to departmental clinical systems, that only see a subset of the patients.
While some systems (paediatrics, maternity, geriatrics) can filter on patient demographics, a number of systems are for cohorts of patients that don't fit a particular criteria.
One of our system vendors has a patient index filter service that keeps a local index of relevant patient identifiers, and only forwards matching messages.