Magnesium (Mg) in Serum is a test used to measure magnesium levels in the blood, an essential mineral that plays a key role in many biological processes, such as regulating muscle and nerve function, protein synthesis, and bone health. Magnesium is also important for converting food into energy and supporting the immune system. This test is recommended to determine whether there is a deficiency or excess of magnesium, both of which can have negative effects on health, such as muscle cramps, heart arrhythmias, and weakened bones. Doctors rely on the test results to assess various health conditions, including kidney disorders, gastrointestinal diseases, and hormonal imbalances.