Potassium

Serum Potassium is the primary intracellular cation, essential for nerve conduction, muscle contraction (especially the heart), and fluid balance. Serum levels are kept within a narrow range, primarily regulated by the kidneys. Abnormal levels (hypokalemia or hyperkalemia) can cause serious cardiac arrhythmias and muscle weakness, resulting from kidney disease, medications (diuretics, ACE inhibitors), hormonal issues, or severe fluid loss.