Final answer:
A baseline serum lithium level and electrolyte levels such as potassium, calcium, and sodium should be measured before starting lithium treatment.
Step-by-step explanation:
Prior to initiation of lithium treatment, a lab test called a baseline serum lithium level should be conducted. This test measures the lithium concentration in the blood and helps determine the appropriate starting dose of lithium for the patient. In addition, electrolyte levels such as potassium, calcium, and sodium should be checked to assess the patient's overall metabolic status and ensure that these levels are within the normal range before starting lithium treatment.