New direct method for measuring red cell lithium.

A new direct method for the measurement of red cell lithium was compared with the indirect method. Good correlation (r = 0.97) was found and the coefficients of variation of the direct and indirect methods were 3.9% and 5.5%, respectively. In the direct method red cells suspended in choline chloride were centrifuged through dibutyl phthalate, which removes plasma adherent to the cells. A haemolysate is made of the sedimented red cells. The lithium concentration of this was measured by atomic absorption spectrophotometry. There are many conflicting reports about the value of red cell lithium, and methodological problems have been proposed as a reason for this. It is suggested that the simpler, more precise direct method described here should be used in future.