Why Is It That People Who Undergo Lithium Therapy Must

Why is it that people who undergo lithium therapy must have regular blood tests?

A) To make sure that there are no chromosomal mutations that occur as a result of the lithium being in the blood.
B) To test for the development of a white blood cell disease called agranulocytosis that can develop in people taking lithium.
C) Because lithium can be toxic to the body, so it is necessary to make sure it is not too present in one's blood.
D) To make sure that the patient is not taking other drugs that can have a lethal interaction with the lithium.