Overview
The comprehensive metabolic panel (CMP) is a set of 14 blood tests used to assess overall metabolic health. It provides insight into fluid and electrolyte balance, kidney and liver function, and blood glucose levels. Patterns of abnormal results often signal underlying issues that may require further evaluation (AACC CMP 2020).
Components Measured in a CMP
- Electrolytes
- Sodium (Na⁺): Regulates fluid balance; found mainly in extracellular fluid.
- Potassium (K⁺): Critical for cardiac function; mostly intracellular.
- Chloride (Cl⁻): Maintains electrical neutrality, often paired with sodium.
- Bicarbonate (HCO₃⁻): Regulates acid-base balance via the kidneys.
- Renal Markers
- BUN (Blood Urea Nitrogen): Reflects protein metabolism and kidney filtration.
- Creatinine (Cr): Indicates renal function; derived from muscle metabolism.
- Liver & Protein Markers
- Total Bilirubin: Byproduct of heme metabolism, processed by the liver.
- Alkaline Phosphatase (ALP): Found in liver and bone; elevated with tissue damage.
- AST (SGOT) / ALT (SGPT): Enzymes associated with liver and muscle injury.
- Total Protein & Albumin: Reflect hepatic synthetic function and nutritional status.
- Other Key Tests
- Calcium (Ca²⁺): Mostly stored in bone; tightly regulated in serum.
- Glucose: Primary energy source, modulated by hormones and nutrition.
Clinical Uses
- General health screening
- Evaluate fluid, electrolyte, and acid-base status
- Investigate symptoms like edema, fatigue, confusion, or arrhythmias
- Monitor acute or chronic illnesses (e.g., heart failure, diabetes, liver/renal disease)
- Assess medication side effects (e.g., statins, diuretics)
Additional Notes
While typically ordered as a panel, each CMP component can be tested individually based on clinical need. Other relevant electrolytes, such as magnesium and phosphate, may be ordered separately (AACC CMP 2020).
Interpretation Highlights
Sodium (Na⁺)
- ↑ >150 mEq/L (Hypernatremia): Often due to dehydration, Cushing syndrome, or high salt intake.
- ↓ <125 mEq/L (Hyponatremia): Linked to fluid overload, SIADH, hypothyroidism, or diuretics.
Note: High glucose can artificially lower sodium—adjust accordingly.
Potassium (K⁺)
- ↑ >6.5 mEq/L (Hyperkalemia): Often due to renal failure, acidosis, or medications like ACE inhibitors.
- ↓ <2.5 mEq/L (Hypokalemia): Common with diuretics, GI losses, malnutrition, or alkalosis.
Pseudohyperkalemia can result from sample hemolysis.
Chloride (Cl⁻)
- ↑ >115 mEq/L: Seen in metabolic acidosis or excessive saline administration.
- ↓ <80 mEq/L: Often due to vomiting, overhydration, or diuretics.
Bicarbonate (HCO₃⁻)
- ↑ >30 mEq/L: Suggests metabolic alkalosis or compensation for respiratory acidosis.
- ↓ <10 mEq/L: Indicates metabolic acidosis, often from diarrhea or renal tubular acidosis.
BUN
- ↑ >100 mg/dL: Suggests renal impairment, GI bleeding, or high protein intake.
- ↓ <7 mg/dL: Typically benign; associated with malnutrition or overhydration.
Creatinine
- ↑ >8 mg/dL: Indicates renal dysfunction, obstruction, or acute tubular necrosis.
- ↓: Rarely concerning; often due to low muscle mass.
Glucose
- ↑ >99 mg/dL (Hyperglycemia): Diabetes, stress, or endocrine disorders.
- ↓ <65 mg/dL (Hypoglycemia): Can result from liver failure, sepsis, insulin overdose, or tumors.
Calcium
- ↑ >10.3 mg/dL: Common in hyperparathyroidism or malignancy.
- ↓ <8.5 mg/dL: May result from hypoalbuminemia, renal failure, or vitamin D deficiency.
Total Bilirubin
- ↑ >1.0 mg/dL: Unconjugated (e.g., hemolysis, Gilbert syndrome) or conjugated (e.g., hepatitis, obstruction).
- ↓: Generally not clinically significant.
Alkaline Phosphatase (ALP)
- ↑: Liver or bone disorders, infections, or pregnancy.
- ↓: Associated with malnutrition or rare genetic conditions.
AST / ALT
- Moderate ↑: Chronic liver disease, heart failure, or muscle injury.
- Marked ↑: Acute hepatitis, toxins, or ischemic liver injury.
Total Protein / Albumin
- ↑ Protein: Inflammation, myeloma, or dehydration.
- ↓ Protein or Albumin: Liver dysfunction, malnutrition, nephrotic syndrome, or dilutional states.
Limitations
- Potassium: May be falsely elevated by hemolysis or delayed processing.
- Bicarbonate: Low readings may result from air exposure or dilution.
- Creatinine: May be falsely low with N-acetylcysteine or after cooked meat ingestion; not sensitive to early kidney damage.
- eGFR: Less accurate in rapidly changing renal function or extremes of muscle mass; pediatric formulas differ (AACC eGFR 2020).
Preferred Specimen
2 mL serum. Allow SST to clot in an upright position for
at least 30 minutes, then centrifuge sample within 2 hours
of collection. Refrigerate.
ContainerType
serum separator tube
Alternate Specimen Requirements
2 mL serum from a plain red top tube. Allow sample to
clot in an upright position for at least 60 minutes, then
centrifuge sample and transfer serum to a plastic transport
tube within 2 hours of collection. Clearly label tube as
serum from a plain red top tube. Refrigerate.
Minimum Volume
2 mL serumTransport Temperature
refrigerated
Specimen Stability
1 day room temperature; 1 week refrigerated
Methodology
Roche COBAS automated methodology or other
automated chemistry method.
References
American Association for Clinical Chemistry (AACC). Comprehensive Metabolic Panel (CMP). AACC website. https://labtestsonline.org/tests/comprehensive-metabolic-panel-cmp. Updated August 12, 2020. Accessed September 2, 2020.
American Association for Clinical Chemistry (AACC). Calcium. AACC website. https://labtestsonline.org/tests/calcium. Updated February 19, 2020. Accessed August 25, 2020.
American Association for Clinical Chemistry (AACC). Electrolytes and Anion Gap. AACC website. https://labtestsonline.org/tests/aldosterone-and-renin. Updated November 13, 2019. Accessed August 14, 2020.
American Association for Clinical Chemistry (AACC). Estimated Glomerular Filtration Rate (eGFR). AACC website. https://labtestsonline.org/tests/estimated-glomerular-filtration-rate-egfr. Updated September 8, 2020. Accessed September 22, 2020.
American Association for Clinical Chemistry (AACC). Total Protein, Albumin-Globulin (A/G) Ratio. AACC website. https://labtestsonline.org/tests/total-protein-albumin-globulin-ag-ratio. Updated August 12, 2019. Accessed September 2 2020.
Biljak VR, Honović L, Matica J, Krešić B, Vojak SŠ. The role of laboratory testing in detection and classification of chronic kidney disease: national recommendations. Biochem Med (Zagreb). 2017 Feb 15;27(1):153-176. doi: 10.11613/BM.2017.01928392738
Freda BJ, Davidson MB, Hall PM. Evaluation of hyponatremia: a little physiology goes a long way. Cleve Clin J Med. 2004;71(8):639-650. doi:10.3949/ccjm.71.8.63915449759
Kapsner CO, Tzamaloukas AH. Understanding serum electrolytes. How to avoid mistakes. Postgrad Med. 1991;90(8):151-161. doi:10.1080/00325481.1991.117011461749730
Lee S, Kang KP, Kang SK. Clinical usefulness of the serum anion gap. Electrolyte Blood Press. 2006;4(1):44-46. doi:10.5049/EBP.2006.4.1.4424459484
Nickson C. Anion Gap. Life in the Fastlane website: https://litfl.com/anion-gap. Update April 23, 2019. Accessed July 16, 2020.
Scott MG, Heusel JW, LeGrys VA, et al. Electrolytes and Blood Gases. In: Burtis CA, Ashwood ER, eds. Tietz Textbook of Clinical Chemistry. 3rd ed. Philadelphia, PA: WB Saunders Co; 1999:1056-92.Diagnostic Role
The comprehensive metabolic panel (CMP) is ordered during both routine health exams and in acute evaluations to identify electrolyte, fluid, metabolic imbalance (acidosis or alkalosis), renal and hepatic function, and/or glucose abnormalities. The CMP is used to screen for conditions such as diabetes, renal disease or hepatic dysfunction, as well as monitor known conditions, such as hypertension (AACC CMP 2020).
Results are evaluated for both individual lab abnormalities as well as together to identify patterns that may identify or suggest underlying pathology, such as dehydration, renal or pulmonary disease, or endocrine abnormalities. A series of CMPs may be followed over time to monitor interventions. If the resulted values do not correlate with clinical findings, hemolysis or laboratory error needs to be ruled out, typically by resubmitting a new blood sample for the laboratory to analyze.