Final answer:
A blood sample to check for lithium levels should be collected 12 hours after the last dose to measure the trough concentration. The sample is collected into lithium heparin tubes and centrifuged to separate plasma for analysis.
Step-by-step explanation:
When taking a patient's blood sample to check for lithium levels after a dose of medication, it is crucial to collect the sample at the correct time. Lithium levels should be drawn usually 12 hours after the last dose to represent the trough or lowest concentration in the patient's bloodstream, which is just before the next dose is due. It is essential for the accuracy of the test that this schedule is adhered to.
Blood samples are collected into tubes containing lithium heparin and centrifuged to obtain plasma. This is a standard procedure in the clinical setting for preparing a sample for various plasma measurements. During the centrifugation process, cellular components are separated from the plasma, allowing for accurate assessment of substances dissolved in the plasma.