What is a basic metabolic panel (BMP) and which analytes does it measure, including their normal reference ranges?

Basic Metabolic Panel: Definition and Components

Core Definition

A Basic Metabolic Panel (BMP) is a blood test that measures seven essential analytes: sodium, potassium, chloride, bicarbonate (or total CO2), glucose, blood urea nitrogen (BUN), and creatinine. 1 This panel provides critical information about electrolyte balance, kidney function, acid-base status, and glucose metabolism. 1

Measured Analytes and Normal Reference Ranges

Electrolytes

• Sodium (Na+): 136-145 mEq/L - Primary determinant of extracellular fluid volume and osmolality 1, 2
• Potassium (K+): 3.5-5.0 mEq/L - Critical for cardiac function and neuromuscular activity 1, 2
• Chloride (Cl-): 98-107 mEq/L - Major extracellular anion, important for acid-base balance 2
• Bicarbonate (HCO3-) or Total CO2: 22-29 mEq/L - Reflects acid-base status and respiratory compensation 1, 2, 3

Metabolites

• Glucose: 70-100 mg/dL (fasting) - Screening marker for diabetes and metabolic disorders 1
• Blood Urea Nitrogen (BUN): 7-20 mg/dL - Reflects protein metabolism and renal function 1, 2
• Creatinine: 0.6-1.2 mg/dL (varies by sex and muscle mass) - Most reliable marker of glomerular filtration rate 1, 2

Clinical Applications

Screening and Monitoring

• Routine preoperative assessment for patients undergoing major surgery, including total joint arthroplasty 1, 4
• Evaluation of resistant hypertension when combined with urinalysis and aldosterone/renin ratio 1
• Monitoring patients on outpatient parenteral antimicrobial therapy (OPAT) with nephrotoxic agents like vancomycin or aminoglycosides 1
• Assessment of elderly patients with multimorbidity to guide medication adjustments and detect complications 1

Risk Stratification

• The BMP demonstrates superior predictive ability for mortality when components are combined into a risk score, with areas under the curve of 0.85-0.89 for predicting death at 30 days, 1 year, and 5 years 5
• Abnormal preoperative BMP values predict postoperative complications requiring medical intervention, particularly in patients with diabetes or chronic kidney disease 4

Important Clinical Caveats

Sample Collection and Processing

• Hemolysis falsely elevates potassium and can affect creatinine measurements on certain analyzers 3
• Icterus interferes with creatinine measurement on some chemistry analyzers but not point-of-care systems 3
• Timing matters: Morning samples are preferred for consistency, particularly when screening for endocrine disorders 1

Interpretation Pitfalls

• Creatinine-based eGFR calculations may be inaccurate in patients with extremes of muscle mass, requiring cystatin C for confirmation 1
• Small changes (±0.3 units) in individual analytes may reflect assay variability rather than true physiological changes 1
• Population-based reference ranges may not apply to athletes or specific ethnic groups, requiring individualized baseline values 1

Overutilization Concerns

• Routine daily BMP testing in stable postoperative patients without major comorbidities generates unnecessary costs without contributing actionable information 4, 6
• Implementation of automated BMP ordering increased total calcium testing by 3-fold without changing diagnosis rates, suggesting excess testing 6
• Targeted BMP ordering based on specific clinical indications (diabetes, chronic kidney disease, abnormal preoperative values, nephrotoxic medications) is more cost-effective than routine screening 4

When to Recheck

• Within 3-7 days for patients with significant baseline electrolyte abnormalities or renal dysfunction (creatinine ≥2 mg/dL or eGFR <30 mL/min/1.73 m²) 7
• Within 2-4 weeks for stable outpatients initiating therapies affecting fluid/electrolyte balance 7
• Weekly monitoring for patients with high-output ostomy or short bowel syndrome due to substantial electrolyte losses 7