comprehensive metabolic panel

**Components (14 tests)** - **Glucose**: fasting normal 70-99 mg/dL; ≥126 fasting suggests diabetes. Also detects hypoglycemia, DKA, and HHS. - **Electrolytes**: Na⁺ (135-145), K⁺ (3.5-5.0), Cl⁻ (98-107), HCO₃⁻ (22-28 mEq/L). - **Renal**: BUN (7-20 mg/dL) and creatinine (0.6-1.2 mg/dL). BUN:Cr >20 suggests prerenal azotemia (volume depletion, heart failure, GI bleed); <15 suggests intrinsic renal disease (ATN). - **Calcium** (8.5-10.2 mg/dL): correct for albumin. Corrected Ca = measured Ca + 0.8 × (4 − albumin). - **Protein**: albumin (3.5-5.0 g/dL; a marker of synthetic function and nutrition) and total protein. - **Liver**: AST, ALT, ALP, and total bilirubin.

**BMP vs CMP** - BMP = glucose, Na, K, Cl, HCO₃, BUN, Cr, Ca (8 tests). - CMP = BMP + albumin, total protein, ALP, AST, ALT, bilirubin (14 tests). - The hepatic function panel is a separate order. It overlaps with the CMP liver tests and adds direct bilirubin.

**Derived values** - **Anion gap** = Na − (Cl + HCO₃). Normal is about 8-12. - High anion gap metabolic acidosis (MUDPILES): methanol, uremia, DKA, propylene glycol, isoniazid/iron, lactic acidosis, ethylene glycol, salicylates. - Normal anion gap (hyperchloremic) acidosis: diarrhea, RTA, saline infusion. - **Hepatic patterns** - Hepatocellular injury: AST/ALT markedly elevated (viral hepatitis, ischemia, acetaminophen toxicity). - AST:ALT >2:1 suggests alcoholic hepatitis. - Cholestatic injury: ALP and bilirubin elevated (biliary obstruction, PBC, PSC). - Low albumin suggests chronic liver disease, nephrotic syndrome, malnutrition, or protein-losing enteropathy. - **Glomerular filtration rate (GFR)**: eGFR is calculated from creatinine, age, and sex (CKD-EPI).

**Clinical pearls** - Hyperkalemia: ECG changes include peaked T waves, widened QRS, and sine wave. Pseudohyperkalemia comes from hemolysis. Treat with calcium gluconate (membrane stabilization), insulin plus glucose, and albuterol. - Hyponatremia: assess volume status and serum osmolality. Correct slowly to avoid osmotic demyelination (central pontine myelinolysis). - Hypercalcemia: "stones, bones, groans, psychiatric overtones." Causes include primary hyperparathyroidism and malignancy. - Ordering: used for routine screening and admission labs. It is also used to monitor drugs with renal or hepatic toxicity (e.g., statins, ACE inhibitors, diuretics). - Interferences: hemolysis falsely raises K⁺, AST, and LDH. Hyperlipidemia or hyperproteinemia causes pseudohyponatremia with indirect ion-selective electrode methods.

**Step 1/2 relevance**: Interpreting CMP abnormalities is a core skill in acid-base questions, AKI workup, liver disease patterns, electrolyte emergencies, and diabetic emergencies.