What laboratory marker is more accurate for magnesium assessment than serum magnesium?

RBC (Red Blood Cell) magnesium is considered a more accurate laboratory marker for assessing magnesium status than serum magnesium because it reflects the magnesium content within the cells, which is critical for cellular functions. Serum magnesium can fluctuate due to various factors, such as hydration status, diet, and acute illness, making it an unreliable indicator of total body magnesium levels.

In contrast, RBC magnesium provides a more stable measure as it indicates the magnesium that is actually available for cellular metabolism and biochemical processes. It provides a clearer picture of magnesium deficiency or sufficiency over a longer period, as it is less affected by short-term changes in serum levels. This makes RBC magnesium a preferred choice in situations where a more precise evaluation of magnesium status is necessary, particularly if clinical suspicion of deficiency exists despite normal serum levels.