[petilon]

Blood tests are pretty useless for magnesium. The deficiency is in cells, magnesium level in blood is not a good test for that deficiency.

[orionsbelt]

They have blood tests for both (serum or RBC):

The Magnesium RBC Test measures magnesium inside red blood cells, providing a more accurate assessment of magnesium status than serum tests.

[m_mueller]

wouldn't a cell deficiency lead to it depleting also the magnesium levels in the blood, simply based on osmosis?

[manoDev]

The organism dumps Mg on the blood as much as necessary because it needs to remain in stable concentrations.

When a serum Mg test comes out low, the patient already has severe deficiency and visible symptoms, so isn’t very useful unless you’re investigating a systemic issue.

As explained by my endocrinologist.

[stouset]

If blood concentrations drop, you die.

[allannienhuis]

what is a good test for magnesium deficiency?

[petilon]

They only have blood tests, and that's not very useful.