A diagnostic system with a handling system that has a loading bay to receive and hold a plurality of carriers. An identification device is configured to identify an identifying feature of the carriers to determine the type of contents loaded on each carrier. A transporter transports the carriers from the loading bay to a first or second location depending on the determined type of contents on each carrier. The transporter has random access to the plurality of carriers in the loading bay. A diagnostic process is conducted using the contents. A carrier, such a for reagents, has one or more holding portions, at least one of which can be moved or rotated with respect to the body of the carrier for mixing or stirring the contents of a container coupled therewith. Also, a retention member can be associated with a positioning device, such as a carousel, to lock and unlock the carrier with respect thereto.