The effect of smoking on the serum ionized magnesium concentration is method-dependent.

Objective: To investigate the effect of smoking on serum ionized magnesium concentration ([Mg2+]) determined by the NOVA and AVL Mg ion-selective electrodes (Mg ISEs).
Methods: Subjects were apparently healthy smokers (n = 30) and nonsmokers (n = 30). We determined NOVA and AVL [Mg2+] in their serum and in test solutions containing compounds increased by smoking. We also determined subjects' white blood cell and differential counts.
Results: For smokers, the mean values for NOVA and AVL [Mg2+] differed significantly (0.41 vs 0.52 mmol/L, respectively). We found a significant intramethod difference in NOVA [Mg2+] (0.11 mmol/L, P < .0001) between smokers and nonsmokers. A dose-dependent decrease in NOVA [Mg2+] was observed with an increase in cigarettes/day. NOVA [Mg2+] inversely correlated with white blood cell counts. There was no interference by the test compounds with either Mg ISE.
Conclusion: Smoking may induce a serum factor, possibly related to white blood cells, that negatively interferes with the response of the NOVA Mg ISE.