Basic Metabolic Panel

Background

The Basic Metabolic Panel (BMP), often referred to as a Chem-7 or SMA-7, is one of the most frequently ordered laboratory tests in the Emergency Department. It provides a rapid assessment of fluid status, electrolytes, renal function, and glucose levels.

Including Calcium technically makes the panel a Chem-8. It differs from the Comprehensive Metabolic Panel (CMP) by the lack of Liver Function Tests (LFTs).

Components and Reference Ranges

Reference ranges vary by laboratory. Typical adult values are listed below.

Component	Abbreviation	Normal Range (US)	SI Units
Sodium	Na	135 – 145 mEq/L	135 – 145 mmol/L
Potassium	K	3.5 – 5.0 mEq/L	3.5 – 5.0 mmol/L
Chloride	Cl	95 – 105 mEq/L	95 – 105 mmol/L
Bicarbonate (Total CO2)	HCO3 / CO2	22 – 29 mEq/L	22 – 29 mmol/L
Blood Urea Nitrogen	BUN	7 – 20 mg/dL	2.5 – 7.1 mmol/L
Creatinine	Cr	0.6 – 1.2 mg/dL	53 – 106 µmol/L
Glucose	Glu	70 – 100 mg/dL (fasting)	3.9 – 5.6 mmol/L
Calcium	Ca	8.5 – 10.2 mg/dL	2.1 – 2.6 mmol/L

Interpretation

Sodium (Na)

• Hyponatremia (<135):
  • <120 mEq/L is a critical value (Risk of Seizure, coma).
  • Assess volume status (Hypovolemic, Euvolemic, Hypervolemic).
  • Pearls: rule out Pseudohyponatremia (Hyperlipidemia/Hyperproteinemia) and Hyperglycemic induced (Corrected Na = Measured Na + 1.6 * [(Glucose - 100) / 100]).
• Hypernatremia (>145):
  • Almost always implies free water deficit (Dehydration).
  • Calculate Free Water Deficit.

Potassium (K)

• Hyperkalemia (>5.0):
  • Emergency: >6.0 or any ECG changes (Peaked T waves, QRS widening, Sine wave).
  • Causes: Renal Failure, Rhabdomyolysis, missed dialysis, Acidosis (shifts K out of cells), Hemolysis (lab error).
• Hypokalemia (<3.5):
  • Causes: Diuretics, GI loss (diarrhea/vomiting).
  • Emergency: Arrhythmias, U-waves, respiratory muscle weakness.
  • Always check and replete Magnesium with K.

Chloride (Cl)

• Generally follows Sodium status.
• Hyperchloremia: Often iatrogenic from large volume Normal saline resuscitation (Non-gap metabolic acidosis).
• Hypochloremia: Gastric outlet obstruction/vomiting (Metabolic alkalosis).

Bicarbonate (CO2)

• Represents total venous CO2 content (mostly HCO3).
• Low (<22): Metabolic Acidosis (most common in ED) or compensation for respiratory alkalosis.
  • Calculate Anion Gap (see below).
• High (>29): Metabolic Alkalosis or compensation for chronic COPD (Respiratory acidosis).

BUN and Creatinine

• Acute Kidney Injury (AKI):
  • Prerenal: BUN:Cr ratio > 20:1. (Dehydration, poor perfusion).
  • Intrinsic: BUN:Cr ratio < 15:1. (ATN, AIN, Glomerulonephritis).
  • Postrenal: Obstruction (Stones, BPH).
• Pearl: Isolated elevated BUN (with normal Cr) is a sensitive indicator for Upper GI Bleed (digested hemoglobin).

Glucose

• Hypoglycemia (<70): AMS, diaphoresis, seizure. Treat with D50/D10.
• Hyperglycemia:
  • >250 with AG Metabolic Acidosis + Ketones = Diabetic Ketoacidosis (DKA).
  • >600 with high osmolarity + no acidosis = Hyperosmolar hyperglycemic state.

Calculations

Anion Gap (AG)

• Used to differentiate causes of Metabolic Acidosis.
• Formula: <math>AG = Na - (Cl + HCO3)</math>
• Normal: 8–12 (varies by assay; >12 usually abnormal).
• High Gap Causes (MUDPILES): Methanol, Uremia, DKA, Paraldehyde, Iron/INH, Lactic Acidosis, Ethylene Glycol, Salicylates.
• Note: Hypoalbuminemia lowers the baseline AG. Corrected AG = Observed AG + 2.5 * (4 - Albumin).

Corrected Sodium (Hyperglycemia)

• Formula: {Corrected Na} = {Measured Na} + 0.016 {Glucose} - 100)

Calcium Correction

• If albumin is low, total calcium appears falsely low.
• Formula: {Corrected Ca} = {Measured Ca} + 0.8 (4 - {Albumin})
• Or check an Ionized Calcium (iCa).

See Also

• Comprehensive Metabolic Panel
• Anion Gap
• Acute Kidney Injury
• Hyperkalemia / Hypokalemia
• Hypernatremia / Hyponatremia