When should a comprehensive metabolic panel (CMP) be ordered and what tests does it include?

Comprehensive Metabolic Panel: Indications and Components

What Tests Are Included in a CMP

A Comprehensive Metabolic Panel includes 14 tests measuring kidney function, electrolytes, glucose, and liver function: sodium, potassium, carbon dioxide, chloride, blood urea nitrogen (BUN), creatinine, glucose, calcium, albumin, total protein, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase, and total bilirubin. 1

• The CMP encompasses all components of a Basic Metabolic Panel (BMP) plus liver function tests, while a BMP focuses only on kidney function, electrolytes, and glucose 2
• Albumin levels assess liver synthetic function and nutritional status, while total protein evaluates overall protein status and liver function 1
• The panel does not include a lipid panel—that requires separate testing for cholesterol, LDL, HDL, and triglycerides 2

When to Order a CMP

Order a CMP when comprehensive metabolic assessment is needed, particularly when liver function evaluation is required or when assessing patients with suspected metabolic disorders, malignancy, or multisystem disease. 2

Specific Clinical Indications for CMP:

• Liver disease assessment: Right upper quadrant pain, suspected overdose, known liver disorder, jaundice, hepatomegaly, or ascites 2, 3
• Cancer workup: Initial evaluation of renal cell carcinoma, myeloproliferative neoplasms, acute leukemia, or suspected tumor lysis syndrome 2, 1
• Cardiovascular conditions: Heart disease evaluation or obesity assessment requiring metabolic markers 2
• Baseline monitoring for biologics: Before initiating ustekinumab or other immunosuppressive therapies 4
• NAFLD screening: High-risk patients with type 2 diabetes or BMI >25 who need liver function assessment 2
• Acute stroke evaluation: To identify underlying metabolic conditions and assess thrombolytic therapy eligibility 2, 1

When BMP Is Sufficient Instead:

• Acute kidney injury without liver disease concern: BMP provides adequate kidney function and electrolyte assessment 2
• Hypertension management: After initiating or titrating antihypertensive therapy, particularly ACE inhibitors, ARBs, or thiazide diuretics—recheck within 2-4 weeks 2
• Advanced chronic kidney disease monitoring (eGFR <30 mL/min/1.73 m²): Close electrolyte monitoring for hyperkalemia risk 2
• Routine glucose monitoring: For diabetes management per American College of Clinical Endocrinologists 2

Clinical Decision Algorithm

For patients with abnormal liver blood tests, do not simply repeat the same panel—determine the underlying cause with a liver aetiology screen unless there is high clinical suspicion of a transient finding. 4

Initial Response to Abnormal Results:

• Obtain thorough history: age, ethnicity, symptoms (jaundice, abdominal pain, weight loss, pruritus), comorbidities, medications (prescribed, over-the-counter, herbal), alcohol intake, metabolic syndrome features, family history 4
• Physical examination: BMI, hepatosplenomegaly, ascites, signs of chronic liver disease 4
• Standard liver aetiology screen (adults): Abdominal ultrasound, hepatitis B surface antigen, hepatitis C antibody with PCR if positive, anti-mitochondrial antibody, anti-smooth muscle antibody, antinuclear antibody, serum immunoglobulins, simultaneous serum ferritin and transferrin saturation 4

Monitoring Frequency:

• After medication changes affecting electrolytes/renal function: Retest within 2-4 weeks; once stable, monitor every 3-6 months 2
• Long-term home parenteral nutrition: Body weight, biochemistry (hemoglobin, ferritin, albumin, CRP, electrolytes, kidney/liver function, glucose) every 3-6 months in stable patients 4
• Biologics monitoring: CBC with differential and CMP at baseline; subsequent monitoring at physician's discretion except infliximab (liver function tests every 3 months initially, then every 6-12 months) 4

Important Caveats

• Screening asymptomatic populations: CMPs have limited value as screening tools in health fairs or asymptomatic individuals—positive predictive value for new diagnosis is only 0.356 5
• Pediatric considerations: In children with none of the 12 clinical variables (right upper quadrant pain, overdose, liver disorder, malignancy, heart disease, jaundice, hepatomegaly, ascites, shock), BMP may suffice with potential cost savings 3
• Normal values don't exclude cirrhosis: Both AST and ALT can be normal even with established cirrhosis; AST:ALT ratio >1 suggests advanced fibrosis/cirrhosis 4
• Neonatal cholestasis: Conjugated bilirubin >25 μmol/L requires urgent discussion with pediatrician 4