The Lithium (Li) test is a blood test that measures the level of lithium in a person’s blood. Lithium is a medication commonly used to treat mood disorders such as bipolar disorder, depression, and mania. The test is used to monitor the therapeutic levels of lithium in the blood and to ensure that the medication is not reaching toxic levels. Lithium can be a difficult medication to manage, as too much lithium can cause toxicity and too little can be ineffective. Therefore, the test is typically done regularly during the initial stages of treatment and then less frequently once a stable dose has been established. A person may also need to have their lithium levels monitored if they experience changes in their kidney function, as the kidneys play a role in the elimination of lithium from the body. Overall, the Lithium test is an important tool for managing mood disorders and ensuring the safe and effective use of lithium as a medication.