Lithium levels in white blood cells and their relationship to observed side effects.

A strong correlation was obtained between white blood cell (WBC) lithium concentrations and the severity of observed side effects in a group of 40 patients receiving prophylactic lithium therapy. However, there was no significant correlation between these levels and the specific side effect of hand tremor, although WBC concentrations were higher in patients with greater tremor. These results contrasted with those for plasma and red blood cell (RBC) lithium concentrations, which showed no relationship to side effects. This suggests that WBC lithium concentrations may be a more sensitive index of side effects than conventional plasma estimations.