Why Do Plasma Levels and Renal Function Need to Be

Why do plasma levels and renal function need to be monitored when taking lithium?

A) To make sure sodium levels are increased to allow for resorption of lithium
B) To ensure lithium is not being reabsorbed through the kidneys,causing lithium toxicity
C) To make sure sodium is allowing for resorption of lithium to increase lithium levels in the body
D) To ensure lithium is being reabsorbed through the liver and remaining in the body to produce its effects