Phloretin-sensitive lithium transport in erythrocytes of affectively ill patients: Intra-individual reproducibility

1.1. The phloretin-sensitive component of lithium (Li+) efflux from erythrocytes has been reported to be significantly reduced in patients with bipolar affective disorders. The value of this finding depends on how reproducible the efflux measurements are. We have therefore investigated the intra-individual day-to-day reproducibility of this parameter, and total erythrocyte Li+ efflux in patients with bipolar affective disorders and in age and sex matched healthy controls.2.2. Six carefully selected, typical bipolar patients and age and sex matched healthy volunteers were studied. These experiments were repeated under identical conditions on 3 occasions within a brief time period (21 days).3.3. We have found that both the total erythrocyte Li+ efflux and the phloretin-sensitive Li+ efflux exhibited considerable day-to-day intra-individual variability in both patients and healthy controls. The standard deviation of total efflux values was as large as ± 31.1% of the mean in some subjects. Mean phloretin-sensitive Li+ efflux for patients was found to be 0.066 ± 0.02 mEq/1 RBC, and for controls 0.048 ± 0.01 mEq/1 RBC, in agreement with values reported in the literature. However, in some individuals standard deviation of this parameter, was as high as ± 50% of the mean. This variation was not the result of the biochemical technique, since all measurements were carried out in duplicate, and these differed less than 5%.4.4. These findings suggest, that in view of the small absolute values of the phloretin-sensitive Li+ efflux, and its considerable day-to-day variation, the relevance of this biochemical parameter to the postulated cell membrane defect in affective disorders should be interpreted with some caution and needs further evaluation.