The measurement of lithium in the blood is useful for monitoring the treatment of patients with bipolar disorder. For lithium to be effective, blood levels must be within a specific range known as the therapeutic window. Measuring lithium levels also prevents adverse effects that can be caused by levels that are too high. With a concentration within the therapeutic window, an improvement is seen in the mood disorders among most patients with manic depressive disorders. At the beginning of treatment, lithium blood testing is generally more frequent in order to obtain the right concentration. This examination is then ordered on a regular basis or when new drugs are introduced. Because lithium is mainly eliminated by the kidneys, physicians will regularly monitor the kidney function of patients under treatment by requesting additional testing. Taking lithium can also disrupt thyroid function, a potential problem that is monitored by assessing the thyroid gland (TSH, etc.). Blood concentration and side effects of lithium can increase if dehydration or salt loss occurs due to heavy sweating or from diseases that cause vomiting or diarrhea.