Correlation between Saliva and Serum Lithium Levels in Manic-depressive Patients

Abstract

The relationship between serum and saliva lithium concentrations was studied in 11 manic-depressive outpatients on chronic lithiurn therapy. Trough serum and saliva lithium levels were measured every three to four weeks during clinic visits for a period of at least 16 weeks. If lithium dosage was changed, serum and saliva levels were measured twice over a three-week period and every three to four weeks ihereafter. A pharmacist rated clinical status of the patients according to level of mania. Intersubject analysis showed a poor correlation between measured serum and saliva lithium levels (r = 0.50); 51 of 109 serum levels estimated from saliva levels differed by 0.18 meq/liter or more from measured serum levels. Intrasubject analysis showed a stronger correlation than did intersubject analysis (p < 0.005). Of 109 serum levels estimated by intrasubject analysis, only 22 differed by 0.18 meq/liter or more from the measured serum levels. In patients with the best clinical scores, the intrasubject correlation between saliva and serum levels was strong (r = 0.72-0.94); serum levels estimated from saliva levels differed by less than 0.09 meq/liter from measured serum levels. The study suggests that patients' saliva levels can be used to estimate serum lithium levels in clinically stabilized manic-depressive patients on prophylactic lithium therapy. In the poorly stabilized patients, serum concentrations should be monitored directly.