A method for distinguishing ionized, complexed and protein-bound Mg in normal and diseased subjects

Since 1932, it has been known that Mg exists in blood in several forms: protein-bound, complexed to certain anions, and ionized. However, there is discrepancy and debate on what these fractions are, how to accurately assess them, and whether they are important in diagnosis and prognosis of disease syndromes. Using the NOVA ISE for IMg2+, a controlled method for ultrafiltration of Mg and atomic absorption spectrophotometry, we have found four distinct fractions of Mg in healthy normal plasma and serum: 1. ultrafilterable Mg (81%) (made up of ionized and complexed); 2. ionized Mg (67%); 3. protein-bound Mg (19%); and 4. complexed Mg (14%). The amount of each fraction appears to depend upon the pathophysiologic state of the patients. Previous observations on the amount of complexed and ionized Mg are at best, only approximations, due to the absence of a device (i.e., ISE) to measure accurately IMg2+.