SODIUM (Na+): The primary extracellular cation responsible for regulating total body water distribution, intravascular volume, osmotic equilibrium, and systemic blood pressure.

POTASSIUM (K+): The major intracellular cation essential for myocardial electrical conduction, cardiac muscle contractility, neuromuscular signal transmission, and acid-base regulation.

CHLORIDE (Cl-): The predominant extracellular anion that works alongside sodium to maintain proper hydration, osmotic pressure, and physiological extracellular fluid neutrality.

BICARBONATE / TOTAL CO2 (OPTIONAL / EXTENDED PANEL): Evaluates buffering capacity and renal-respiratory acid-base equilibrium to identify systemic metabolic acidosis or alkalosis.