Pathophysiology
Clinical meaning
The comprehensive metabolic panel (CMP) includes 14 tests evaluating renal function (BUN, creatinine, eGFR), electrolytes (Na+, K+, Cl-, CO2/bicarbonate, calcium), glucose, and hepatic function (total protein, albumin, bilirubin, AST, ALT, ALP). Interpreting the CMP requires understanding of the physiological systems each test reflects. Sodium reflects water balance (hyponatremia is usually dilutional, not sodium depletion). Potassium homeostasis is maintained by aldosterone (renal excretion), insulin (cellular uptake), and acid-base status (acidosis shifts K+ extracellularly). The anion gap (Na - Cl - HCO3; normal 8-12) identifies the cause of metabolic acidosis: elevated gap indicates acid accumulation (MUDPILES: Methanol, Uremia, DKA, Propylene glycol, INH/Iron, Lactic acidosis, Ethylene glycol, Salicylates); normal gap indicates bicarbonate loss (diarrhea, RTA).