Magnesium RBC

This blood test evaluates the level of magnesium in red blood cells for deficiency or toxicity.
Magnesium is a mineral that plays an important role in many biochemical reactions including your heartbeat, nerve and muscle function, bone development, energy production, glucose and blood pressure regulation and protein synthesis.
The Magnesium Test is often used to monitor individuals with kidney disorders or disease, or to evaluate individuals with symptoms of malnutrition or malabsorption.
The RBC magnesium test is very similar to the serum test, but it measures the amount of magnesium in red blood cells rather than the magnesium in the blood serum. The RBC test is viewed as more accurate than the serum test because when you are deficient in magnesium, your body takes it from cells instead, therefore, making it highly detectable through an RBC. The RBC may indicate that these red blood cells are missing a healthy level of magnesium, meaning you may have a magnesium deficiency. 
Deficient magnesium levels can lead to:
Muscle cramps/spasms/tremorsFatigue/SomnolenceDecreased reflexesHeart blockInexplicably low calcium levelsNauseaLoss of appetiteSeizuresHeart arrhythmiaDiarrheaMagnesium levels that are high can be a sign of:
Renal (kidney) failureIngesting large amount of antacidsAddison diseasePregnant patients with pre-eclampsia or eclampsia on anticonvulsant drugsMagnesium deficiency can be more prevalent in people who:
Drink caffeinated drinks or alcohol oftenHave malabsorption of vitamin D, which aids in magnesium absorptionAre uncontrolled diabeticsEat a lot of refined sugar, which causes the body to excrete magnesium through the kidneysHave Bartter syndrome or Gitelman syndromeAre on corticosteroidsMajor dietary magnesium sources include:
Leafy green vegetables like spinachSquashPumpkin seedsNuts and seedsLegumesFishWhole grains