[Clinical relevance of lithium determination in RBC: results of a catamnestic study (author's transl)].

In 34 out-patients Li+- and K+-concentrations were determined in plasma and RBC during 15 months of clinical routine observations. Average frequency of check-ups was 9/patient. Psychopathological state and side effects were documented by the AMP-system. The mean intra-extracellular lithium concentration ratio (LiQ) was 34%. The ratio and the absolute lithium RBC concentration showed a wide intraindividual variability between 5 and 53%. Patients under 50 years old had the same absolute concentration values as the older ones but required a 50% higher average dose. Side effects such as tremor and thirst correlated well the intra-extracellular ratio. No difference was found between unipolar and bipolar depressions. LiQ was slightly reduced and KQ increased in patients with severe relapses or additional psychotropic medication.