Correlation between concentrations of magnesium, zinc, and potassium in plasma, erythrocytes and muscles

In 93 patients, consecutively subjected to laparotomy, we studied the correlation between concentrations of magnesium, zinc and potassium in plasma, erythrocytes and muscle tissue. Sixteen percent had hypomagnesemia, 27% hypozincemia, and 53% hypokalemia. There was no difference with regard to the concentration of magnesium and zinc in erythrocytes or in muscle tissue between patients with low and patients with normal/high plasma concentrations of these minerals. Potassium concentration per liter erythrocytes was slightly but significantly higher in patients with hypokalemia than in patients with normal plasma potassium. When expressed per mmol haemoglobin there was, however, no difference in erythrocyte potassium between these two groups. Neither did they differ with regard to potassium concentration in muscles. There was a highly significant correlation between the concentrations of magnesium, zinc and potassium in erythrocytes as well as in muscle tissue, and a significant correlation between magnesium and potassium in plasma. However, no correlation was found between the mineral concentrations in plasma, erythrocytes and muscles, neither for magnesium, nor for zinc or potassium. We therefore conclude that a valid test to estimate total body stores of these minerals cannot be based on analysis of erythrocytes.