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).
Diagnosis & workup
Diagnostics & workup: - Electrolytes: Na+ (135-145), K+ (3.5-5.0), Cl- (96-106), CO2/bicarb (22-28); derangements indicate fluid/acid-base/hormonal disorders - Renal function: BUN (7-20), Creatinine (0.7-1.3 male, 0.6-1.1 female), eGFR; BUN/Cr ratio >20:1 suggests prerenal azotemia - Glucose: fasting 70-99 normal, 100-125 prediabetes, ≥126 diabetes; random ≥200 with symptoms = diabetes - Hepatic panel: AST/ALT (aminotransferases indicating hepatocellular injury); ALP (cholestatic/biliary obstruction); bilirubin (direct/indirect for conjugated/unconjugated); albumin (synthetic function) - Anion gap calculation: Na - (Cl + HCO3); normal 8-12; elevated gap acidosis (MUDPILES) vs normal gap acidosis (bicarbonate loss) - Calcium: total calcium must be corrected for albumin; corrected Ca = total Ca + 0.8 × (4.0 - albumin); ionized calcium is more accurate