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Excerpt 2
James W. Jefferson, MD and John H. Greist, MD

Lithium & Bipolar Disorder: A Guide

(Excerpt 2)

Why are lithium blood tests necessary? A lithium blood test may also be called a "lithium level," "a serum lithium level," or a "plasma lithium level." This test is important because it enables the doctor to monitor the amount of lithium present in the bloodstream, which is a good guide to the amount of lithium present throughout body tissues. Too little lithium is not effective in stabilizing mood swings, whereas too much may lead to unwanted and sometimes serious side effects. So a lithium blood test helps in two ways: to ensure that the dose of lithium is effective, and to ensure that the dose of lithium is safe.

A lithium blood level that is both safe and effective is called a "therapeutic" level. Higher therapeutic levels may be necessary to treat acute episodes. This level varies among individuals but generally is between 0.8-1.2 milliequivalents per liter (mEq/l) for acute episodes and 0.6-1.0 mEq/l for preventive use. Many people do well at levels between 0.6-0.8 mEq/l and some between 0.4-0.6 mEq/l. At blood levels higher than therapeutic, lithium is unlikely to be any more effective but does begin to cause more side effects. At blood levels below therapeutic, lithium may be less likely to be helpful. People taking lithium should ask their doctors what their lithium levels are and how to interpret them. (Page 32 of this booklet provides a convenient place for recording lithium doses and blood levels.)

Remember that the lithium blood level is only one of the aids used by the doctor to determine proper lithium dose. The most important guide to proper dose is how the person taking lithium is feeling and functioning.

People sometimes wonder why lithium therapy requires blood tests while therapy with many other drugs (aspirin, penicillin, cold tablets, for example) does not. There are several reasons. First, lithium is a drug that can be easily measured in the blood. Next, people�s bodies handle a given dose of lithium quite differently due to variations in absorption into the bloodstream, distribution to the body tissues, and excretion from the body by the kidneys. Thus, the same oral dose of lithium may produce quite different blood levels in different individuals. Finally, lithium differs from many other drugs in that the amount needed to be effective is close to the amount that can produce toxicity (sickness caused by too much medication). Knowing the blood level helps the doctor adjust the dose to avoid toxicity while maintaining therapeutic benefit.