Basic Metabolic Panel

Background

The Basic Metabolic Panel (BMP) is a standard diagnostic test used to evaluate fluid balance, electrolyte status, and renal function. It typically includes measurements of sodium, potassium, chloride, bicarbonate, blood urea nitrogen (BUN), creatinine, and glucose.

When calcium is included, the panel is often referred to as a "Chem-8." Interpretation of these values allows for the rapid identification of metabolic abnormalities, renal failure, and diabetic emergencies.

Components and Interpretation

Sodium (Na)

• Normal Range: 135–145 mEq/L
• Hyponatremia (<135):
  • Evaluate volume status (hypovolemic, euvolemic, hypervolemic).
  • Monitor for neurological sequelae (seizure, coma) if drop is acute or severe (<120 mEq/L).
• Hypernatremia (>145):
  • Indicates free water deficit relative to sodium.
  • Associated with dehydration or diabetes insipidus.

Potassium (K)

• Normal Range: 3.5–5.0 mEq/L
• Hyperkalemia (>5.0):
  • Emergency: Values >6.0 mEq/L or ECG changes (peaked T waves, QRS widening) require immediate calcium stabilization and shifting agents (insulin/dextrose).
  • Common etiologies: Renal failure, acidosis, hemolysis (pseudohyperkalemia), or medications.
• Hypokalemia (<3.5):
  • Emergency: Risk of arrhythmias and respiratory muscle weakness.
  • Common etiologies: GI losses (vomiting/diarrhea), diuretics, or intracellular shifts.

Chloride (Cl)

• Normal Range: 95–105 mEq/L
• Primarily used to assess acid-base status and anion gap.
• Hyperchloremia: Often associated with aggressive normal saline resuscitation (non-gap metabolic acidosis).
• Hypochloremia: Associated with metabolic alkalosis (e.g., vomiting, gastric suction).

Bicarbonate (CO2)

• Normal Range: 22–29 mEq/L
• Measures total venous CO2 content, serving as a proxy for serum bicarbonate.
• Low (<22): Suggests Metabolic Acidosis (calculate Anion Gap) or respiratory alkalosis compensation.
• High (>29): Suggests Metabolic Alkalosis or respiratory acidosis compensation (e.g., COPD).

BUN and Creatinine

• BUN (7–20 mg/dL) and Creatinine (0.6–1.2 mg/dL)
• Reflect renal clearance and glomerular filtration rate (GFR).
• Acute Kidney Injury (AKI):
  • Defined by acute rise in Creatinine.
  • BUN:Cr Ratio > 20:1 suggests prerenal etiology (dehydration) or upper GI bleed.

Glucose

• Normal Range (Fasting): 70–100 mg/dL
• Abnormalities:
  • Hypoglycemia: Critical when <70 mg/dL with symptoms.
  • Hyperglycemia: Assess for Diabetic Ketoacidosis (DKA) or Hyperosmolar Hyperglycemic State (HHS) in patients with diabetes.

Calcium (Total)

• Normal Range: 8.5–10.2 mg/dL
• Inclusion of calcium in routine panels (creating the Chem-8) aids in detecting hyperparathyroidism or malignancy, though it may lead to increased downstream testing without changes in diagnosis prevalence.
• Correct for low albumin or check ionized calcium if status is unclear.

Calculations

Anion Gap

Used to evaluate metabolic acidosis.

• Formula: <math>\text{AG} = \text{Na} - (\text{Cl} + \text{HCO}_3)</math>
• Normal: 8–12 mEq/L.
• High AG is associated with MUDPILES etiologies (e.g., DKA, uremia, toxic alcohols).