Comparison between saliva and serum lithium concentrations in patients treated with lithium carbonate

The relation between serum and saliva lithium concentration was studied in patients treated with lithium carbonate. In 23 patients a highly variable saliva/serum ratio was found in simultaneous saliva and serum samples. In five patients studied during a period of 4-8 weeks three patients showed a high fluctuation in saliva/serum lithium ratio. In 20 patients saliva lithium concentrations varied unexpectedly in a second sample produced after 15 min. Although some authors report a high and stable relation between saliva and serum lithium concentration, we consider the saliva lithium level unreliable as a prediction of the serum lithium level in patients treated with lithium carbonate.