Define indicators of Mg status - Total Serum Mg?

Several indicators of Mg status have been described.

i) Total Serum Mg: Serum Mg concentration are routinely measured to assess its status. However, extracellular Mg represents only 1% of the total Mg and appears to be homeostatically regulated. Normal serum levels may occur despite intracellular deficit, But when serum Mg is below normal, the intracellular Mg is definitely lower. Thus, low serum levels can help to detect advanced Mg deficiency. It is suggested that level of ionized Mg may. be more reliable and relevant determinant of deficiency than the total serum Mg, as protein bound Mg is subjected to more variations.