​RBC Magnesium (Red Blood Cell Magnesium)
Produced by: Not produced but absorbed through the gastrointestinal tract.
Definition / Purpose: Regarding the thyroid gland, the mineral magnesium is responsible for converting inactive T4 into active T3.
Lab Reference Range: 4.0-6.4 mg/dL
When to order:

• Screening test that should be ordered when looking for thyroid disease.
• Follow up lab testing to confirm normal levels.

Pearls:
Half-life: Not applicable.
Magnesium levels may be more accurate when testing with hair analysis or by utilizing micronutrient testing through Spectracell Labs.
Patients with low magnesium may not be able to tolerate normal doses of thyroid hormone replacement therapy and may experience heart palpitations and fluttering. Seek medical attention.