Saliva lithium: a poor predictor of plasma and erythrocyte levels

Lithium levels were measured in plasma, erythrocytes and saliva in 28 patients to determine the accuracy of saliva lithium as a predictor of plasma and erythrocyte levels. The range and mean lithium levels (mmol/L) found in the three compartments were as follows: plasma, mean = 0.72, range 0.17-1.33; erythrocyte, mean = 0.33, range 0.03-0.7; saliva, mean = 1.21, range 0.36-3.9. High levels of inter-individual and intra-individual variation were found in plasma/saliva and erythrocyte/saliva lithium level ratios. We recommended that saliva lithium measurements should not be used to monitor lithium therapy.