When should I order a comprehensive metabolic panel (CMP) instead of a basic metabolic panel (BMP)?

When to Order a Comprehensive Metabolic Panel (CMP) vs Basic Metabolic Panel (BMP)

Order a CMP when you need liver function assessment in addition to kidney function and electrolytes; order a BMP when you only need to evaluate kidney function, electrolytes, and glucose. 1, 2

Panel Components

BMP includes 8 tests:

• Glucose, sodium, potassium, chloride, carbon dioxide (bicarbonate), blood urea nitrogen (BUN), creatinine, and calcium 1

CMP includes all BMP tests PLUS 6 additional liver function tests:

• Albumin, total protein, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase, and total bilirubin 1, 2

Clinical Situations Requiring CMP

Order a CMP in these specific scenarios:

• Initial cancer workup including renal cell carcinoma, myeloproliferative neoplasms, or acute leukemia 2
• Suspected liver disease including right upper quadrant pain, jaundice, hepatomegaly, ascites, or known liver disorder 2
• Drug overdose evaluation where hepatotoxicity is a concern 2
• Obesity assessment requiring comprehensive metabolic evaluation including liver function 2
• Tumor lysis syndrome requiring comprehensive metabolic monitoring 2
• Post-nephrectomy follow-up for renal cell carcinoma 2
• NAFLD screening in high-risk patients (includes ALT, AST, and bilirubin) 2
• Acute stroke evaluation when underlying liver conditions may be contributing 2
• Multisystem inflammatory syndrome in children (MIS-C) as part of tier 1 screening 1

Clinical Situations Requiring Only BMP

Order a BMP in these specific scenarios:

• Hypertension management when monitoring electrolytes and kidney function after initiating or titrating antihypertensive medications (check within 2-4 weeks) 3
• ACE inhibitor or ARB initiation - check potassium and creatinine 2 weeks after starting 3
• Diabetes monitoring for glucose control without liver concerns 1
• Routine electrolyte monitoring in patients on diuretics, especially thiazides (check within 4 weeks of initiation or dose escalation) 3
• Acute kidney injury evaluation when liver function is not a concern 3
• Postoperative monitoring after total joint arthroplasty in patients with diabetes, chronic kidney disease, or abnormal preoperative values 4

Key Decision Points

Choose CMP over BMP when:

• Any suspicion of liver dysfunction exists 2
• Comprehensive nutritional assessment is needed (albumin, total protein) 1
• Initial workup for malignancy 2
• Patient has heart disease requiring comprehensive metabolic assessment 2

Choose BMP over CMP when:

• Only monitoring kidney function and electrolytes 1, 2
• Following patients on medications affecting potassium (ACE inhibitors, ARBs, aldosterone antagonists) 3
• Cost containment is important and liver function assessment is not clinically indicated 4

Important Caveats

• A CMP does NOT include a lipid panel - this must be ordered separately if needed for cardiovascular risk assessment 2
• Routine daily metabolic panels are often unnecessary - in postoperative patients without major comorbidities or abnormal preoperative values, routine BMP testing does not contribute actionable information and represents unnecessary cost 4
• Frequency of monitoring matters - after medication changes affecting electrolytes or kidney function, recheck within 2-4 weeks; once stable, every 3-6 months is appropriate 3
• In advanced CKD (eGFR <30 mL/min/1.73 m²), continue monitoring electrolytes closely as adaptive mechanisms begin to fail and hyperkalemia risk increases 3