Del. Code tit. 18, § 3585

The utilization review entity may not revoke, limit, condition or restrict a pre-authorization on ground of medical necessity after the date the health-care provider received the pre-authorization. Any language attempting to disclaim payment for services on the basis of changes to medical necessity that have been pre-authorized and delivered while under coverage shall be null and void. A proper notification of policy changes validly delivered as per § 3372 of this title may void a pre-authorization if received after pre-authorization but before delivery of the service.