Serum electrolyte testing (sodium Na, potassium K, magnesium Mg, chloride Cl) measures the concentration of these charged metal ions in the liquid part of the blood. These electrolytes play a crucial role in maintaining osmotic balance, acid-base (pH) balance, and transport across cell membranes. They are essential for vital functions such as nerve transmission, muscle contraction (including cardiac muscle), and blood pressure regulation. This test is used to assess a wide range of conditions, from mild dehydration to serious kidney and heart disorders.