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Erythrocyte and plasma potassium, magnesium, sodium and calcium were estimated before and after dialysis in 32 studies on 14 patients undergoing recurrent haemodialysis. Predialysis erythrocyte magnesium was raised while sodium and calcium were depressed. Erythrocyte potassium varied depending on the total body potassium status of the patient. During dialysis erythrocyte potassium and magnesium fell but sodium and calcium increased. Changes in erythrocyte water or blood pH did not account for the shift of erythrocyte cations during dialysis. With recurrent dialysis changes in erythrocyte cations reflected the cumulative effect of individual dialysis and were towards a normal erythrocyte electrolyte composition. Erythrocyte magnesium resisted depletion despite low serum levels. Low dialysate magnesium levels (0.3–0.5 mg/100 ml) are required to maintain near normal serum and cellular magnesium concentrations.

Total body, Erythrocyte and Serum potassium changes during haemodialysis were studied on 29 occasions in 15 patients on maintenance dialysis with a low dialysate potassium concentration (1 mEq/l). The loss in total body potassium during haemodialysis (measured with a whole body counter) varied widely and was significantly related to the pre-dialysis body potassium state of the patient as assessed by total body potassium per kg body weight in spite of a constant high serum to dialysate concentration gradient in all patients. Serum potassium levels did not correlate well with changes in total body potassium or erythrocyte potassium. Erythrocyte potassium was shown to be a reliable and useful index of the direction and magnitude of changes in total body potassium during haemodialysis.

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