Prospective use of saliva lithium determinations to monitor lithium therapy.

A mathematical equation (y = 2.27x -0.45) relating saliva (y) to plasma (x) lithium concentrations was previously determined by one of the authors. A prospective study is reported here in which the correlation coefficient between the predicted and the observed plasma concentrations in a new group of 25 patients was r = 0.89 (p less than 0.001). The study demonstrates that saliva lithium determinations can be safely used to monitor lithium therapy.