A hospital registry is allowed to provide follow-up and treatment information to another hospital registry when what condition is met?

The correct answer focuses on the essential condition that allows for the sharing of follow-up and treatment information between hospital registries: prior contact with the patient. When both registries have documented prior contact with the same patient, it establishes a necessary relationship that justifies the sharing of sensitive health information. This principle is grounded in patient privacy rights and confidentiality agreements, ensuring that information is only exchanged between entities that have a legitimate interest in the patient's care and history.

In scenarios where registries do not have prior contact with the patient, sharing data could potentially violate privacy regulations and ethical standards, as there would be no established basis for exchanging that information. Establishing a relationship through prior contact ensures that both registries are in a position to know the context of the patient's treatment history and to responsibly utilize that information for their respective purposes.

The other choices, while they may seem relevant, do not address the fundamental issue of patient consent and confidentiality necessary for sharing sensitive medical information.