Complete Metabolic Panel Components
A complete metabolic panel (CMP) includes 14 measurements: sodium, potassium, chloride, carbon dioxide (bicarbonate), blood urea nitrogen (BUN), creatinine, glucose, calcium, albumin, total protein, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase, and bilirubin. 1
Core Electrolytes and Minerals
- Sodium - reflects fluid balance and is a critical marker for volume status 2
- Potassium - essential for cardiac function and acid-base homeostasis 2
- Chloride - impacts acid-base balance and renal function 2
- Carbon dioxide (bicarbonate) - assesses acid-base status 1
- Calcium - important for multiple physiologic processes 1
Kidney Function Markers
- Blood urea nitrogen (BUN) - reflects renal function and protein metabolism 2
- Creatinine - the primary marker for estimating glomerular filtration rate (GFR), though it has significant limitations in elderly patients and those with reduced muscle mass 3, 4
Critical Context for Impaired Renal Function
In patients with elevated creatinine, serum creatinine alone is an inadequate screening test for renal failure, particularly in elderly patients, because it underestimates the degree of renal impairment due to reduced muscle mass. 3
- Estimated GFR should be calculated using the CKD-EPI equation (preferred) or Cockcroft-Gault formula rather than relying on serum creatinine values alone 1
- Creatinine levels of 1.3-1.5 mg/dL in men or 1.2-1.4 mg/dL in women indicate subclinical organ damage and warrant GFR estimation 1
- Serum creatinine >1.5 mg/dL in men or >1.4 mg/dL in women contraindicates metformin use due to lactic acidosis risk 1
Glucose Metabolism
- Glucose - screens for diabetes and monitors glycemic control 1
- Fasting glucose 5.6-6.9 mmol/L (102-125 mg/dL) indicates impaired fasting glucose 1
Protein Status
- Albumin - assesses nutritional status and liver synthetic function 1
- Total protein - evaluates overall protein balance 1
Liver Function Enzymes
- AST (aspartate aminotransferase) - hepatocellular injury marker 1
- ALT (alanine aminotransferase) - more specific for liver injury 1
- Alkaline phosphatase - cholestatic liver disease and bone metabolism 1
- Bilirubin - liver function and hemolysis marker 1
Essential Caveats for Renal Impairment
When evaluating patients with elevated creatinine, additional testing beyond the standard CMP is mandatory:
- Urinalysis with albumin-creatinine ratio (ACR) should be obtained, as ascertainment of chronic kidney disease from GFR alone without albuminuria is generally not acceptable 1
- Repeat creatinine testing is essential to verify results and determine if renal failure is acute or chronic 5
- Consider exogenous factors that can falsely elevate creatinine, including creatine supplements and dietary protein intake 6
- Renal ultrasound should be performed to assess kidney size (indicating chronicity) and exclude obstruction 5
For patients with eGFR 45-59 mL/min/1.73 m² without other markers of kidney damage, measuring cystatin C can provide confirmatory evidence of chronic kidney disease. 1