Q: Please explain the therapeutic range level of lithium and it's significance for management of the illness.
Dear Cindy --
Answer: several large research studies have been done looking at relapse rates and relating those rates to people's blood levels at the time. In the biggest such study, the one that really defined the bottom of this range, patients with levels of 0.7 and up had significantly lower relapse rates than those with 0.5 and less. So generally in bipolar I, we shoot for a blood level of 0.7 or higher to be sure the person is protected, as best we can tell from these studies.
The "top end" of this range is defined by the level at which "toxic" symptoms begin to emerge: severe nausea, vomiting, confusion, unsteadiness of gait. This usually does not happen at levels less than 1.2, although I've seen it once in a while as low as 1.0.
Some labs print out different ranges of "therapeutic" (e.g. 0.5 - 1.1; I've even seen 1.5 on some lab sheets) but what really matters is the above logic in defining those upper and lower numbers, not the absolute value the lab chooses.
Finally, note that if a person has continuous symptoms, you can basically forget about the lower number, because you're going to go by their symptoms, not some reference range, in deciding what is enough; however, she or he still needs lab testing to make sure that her/his blood level doesn't go too high. This is generally the case in bipolar II -- i.e. labs are solely for protecting against overshoot, not for determining "enough".