Blood lithium concentration, a laboratory indicator, is generally used in the course of treatment with lithium preparations such as lithium carbonate in patients with bipolar disorder. Because the therapeutic and toxic doses of lithium carbonate are close to each other, the clinical use of this drug requires periodic dynamic testing of blood lithium concentrations, with different normal ranges for different treatment periods. In the acute treatment period, the normal range of blood lithium concentration is 0.6-1.2 mmol/L, in the maintenance treatment period, the normal range of blood lithium concentration is 0.4-0.8 mmol/L. When elderly patients are treated with lithium carbonate, the normal range of blood lithium concentration should not exceed 1.0 mmol/L. During the treatment with lithium carbonate, if the blood lithium concentration exceeds 1.5 mmol/L, the expression may be faint. In the process of lithium carbonate treatment, if the blood lithium concentration exceeds 1.5 mmol/L, there may be symptoms of toxicity such as indifference, fatigue, frequent vomiting, diarrhea, hyperreflexia, involuntary movements of the limbs, etc. When the blood lithium concentration is above 2.0 mmol/L, serious toxic reactions may occur, manifesting as blurred consciousness, slurred vomiting, uncoordinated body movements, seizures and even coma, shock, renal impairment and other adverse consequences. When the blood lithium concentration rises above 3.0mmol/L, it can even endanger the patient’s life.