How does Doxtor know which tubes to collect?

From the tests on the order. Doxtor groups the tests by the tube or container the laboratory needs, and shows one row for each: which kind, how many, and which tests it is for. Volumes are shown only where the laboratory has confirmed them.

If a test’s collection requirement is not known, Doxtor says so before anyone collects, and asks the team to check with the laboratory. How sample requirements are worked out explains the rules.