Red blood cell Li+ to plasma Li+ ratios. Are they related to plasma Li+ concentrations?

The relationship between the lithium ratio (ratio of lithium in blood cells to that in plasma) and plasma lithium concentration was examined in a group of male inpatients taking lithium carbonate for affective disorders. The lithium ratio was found to increase in the majority of these patients as plasma lithium concentration increased. However, the magnitude of variation of the lithium ratio with plasma lithium concentration observed in these patients is not sufficient to seriously affect the value of determining the lithium ratio in the clinical situation.