The A1c test works by measuring the hemoglobin A1c level. Hemoglobin is stored in the red blood cells. When glucose levels are high, the sugar starts to combine with the hemoglobin. It takes the body 8 to 12 weeks to bring hemoglobin A1c levels back to normal. Therefore, if hemoglobin A1c levels are high, that means that there has been a high level of glucose in the blood over the last 2 to 3 months.

A Magnesium RBC test can provide an earlier indicator of magnesium deficiency that a standard magnesium blood test. When levels are low, the body will pull magnesium from the cells to keep blood levels normal. In this case, a magnesium blood test may show normal levels while a magnesium RBC test will give a more accurate result.