Final answer:
Baseline labs before initiation of lithium involve collecting blood samples into tubes containing lithium heparin to obtain plasma.
Step-by-step explanation:
The question is discussing baseline labs that are done before the initiation of lithium. Blood samples are collected into tubes containing lithium heparin and centrifuged to obtain plasma. The quantification of plasma levels of gabapentin is also mentioned, which is unrelated to the question about baseline labs for lithium. The list of elements at the end includes lithium, along with other elements, but it is not directly related to the question either.