Comprehensive Metabolic Panel (CMP): The 14 Numbers on Your Blood Test Explained
The CMP shows kidney function, liver function, electrolytes and glucose in a single tube. Learn what every number means, which pairs matter more than singles, and which patterns point where.
A CMP is 14 chemistry values that describe kidney function (BUN, creatinine, eGFR), electrolytes (sodium, potassium, chloride, bicarbonate), acid-base (anion gap), glucose, calcium, liver enzymes (ALT, AST, ALP, bilirubin) and protein status (albumin, total protein). The clinical value comes from PATTERNS — sodium with bicarbonate, BUN-to-creatinine ratio, ALT with AST — not from any single number in isolation.
The comprehensive metabolic panel (also called Chem-14) is the workhorse of general medicine. Sodium and potassium reflect fluid balance and the neuromuscular safety envelope; bicarbonate and chloride complete the picture and reveal acidosis/alkalosis. BUN and creatinine together stage kidney function and hydration (a BUN:creatinine ratio > 20 suggests pre-renal azotaemia). Glucose provides opportunistic screening for diabetes. Calcium requires albumin correction. ALT is more liver-specific than AST; a ratio > 2 traditionally suggests alcohol-related liver injury. Alkaline phosphatase and bilirubin reveal cholestasis. Albumin < 3.4 g/dL is malnutrition or protein-losing states. Interpret patterns, not singletons.
- Sodium
- 135 – 145 mmol/L
- Potassium
- 3.5 – 5.0 mmol/L
- Creatinine
- 0.6 – 1.3 mg/dL (varies with muscle mass)
- Glucose (fasting)
- < 100 mg/dL
- ALT
- < 40 U/L (F), < 50 U/L (M)
- Albumin
- 3.5 – 5.0 g/dL
The 14 numbers, grouped by system
Kidney panel (BUN, creatinine): urea nitrogen (BUN) and creatinine both rise when the kidneys clear less. Creatinine is more specific to filtration; BUN is influenced by hydration, protein intake, and gastrointestinal bleeding. A BUN:creatinine ratio above 20 in a patient with a rising creatinine suggests pre-renal azotaemia (dehydration, heart failure, GI bleeding).
Electrolytes (Na, K, Cl, HCO₃): sodium reflects total body water balance more than sodium intake. Potassium sits in a very narrow safety window — values below 3.0 or above 5.5 can cause dangerous arrhythmias. Chloride and bicarbonate together reveal acid-base disturbances.
Glucose: a random glucose > 200 with symptoms, or a fasting glucose ≥ 126 confirmed on repeat, meets ADA criteria for diabetes.
Calcium: reported total calcium requires correction for albumin (add 0.8 mg/dL for every 1 g/dL below normal albumin). Ionised calcium is the truer physiological measure.
Liver enzymes (ALT, AST, ALP, bilirubin): ALT is highly liver-specific. AST also comes from muscle, so a raised AST after intense exercise or trauma is not necessarily liver. ALP rises in cholestasis and in bone disease. Bilirubin above 2 mg/dL usually shows visibly as jaundice.
Proteins (albumin, total protein): albumin < 3.4 g/dL points to malnutrition, chronic disease, nephrotic syndrome, or liver failure. Total protein minus albumin gives an estimated globulin fraction — very high globulins (> 4 g/dL) can point to multiple myeloma.
Common CMP patterns and what they suggest
| Pattern | Suggestive of | What to check next |
|---|---|---|
| Low Na + low K + low Cl + high HCO₃ | Vomiting or diuretic use | Medication review, urine chloride |
| Low HCO₃ + high anion gap | Metabolic acidosis (DKA, uraemia, lactic acidosis) | Ketones, lactate, glucose |
| High BUN, normal creatinine | Dehydration or upper GI bleeding | Hydration status, stool test |
| High ALT and AST (ALT > AST) | Non-alcoholic fatty liver, viral hepatitis | Hepatitis serology, ultrasound |
| AST > 2× ALT | Alcohol-related liver injury | Alcohol history, GGT |
| High ALP + high bilirubin | Cholestasis or biliary obstruction | GGT, ultrasound abdomen |
| Low albumin + high globulin | Multiple myeloma, chronic inflammation | SPEP, immunoglobulins |
The pairs that matter most
BUN-to-creatinine ratio: normally 10–15. Above 20 suggests pre-renal azotaemia (dehydration, heart failure); below 10 suggests intrinsic kidney injury or liver failure.
ALT-to-AST ratio: viral or fatty liver disease tends to raise ALT more than AST. Alcohol reverses this — AST > 2× ALT is a classic alcohol clue. Muscle disease raises AST alone.
Sodium-to-glucose interaction: for every 100 mg/dL rise in glucose above normal, measured sodium falls by roughly 1.6 mmol/L. Correct for glucose before diagnosing hyponatraemia in hyperglycaemic patients.
Calcium-albumin: total calcium reported by the lab must be adjusted for albumin. Add 0.8 mg/dL for every 1 g/dL of albumin below 4.0. A "normal" total calcium in a hypoalbuminaemic patient can mask hypercalcaemia.
The anion gap in plain English
Anion gap = Sodium − (Chloride + Bicarbonate). Normal is 8–12. A high anion gap acidosis is one of the most useful patterns in emergency medicine. The classic causes (mnemonic MUDPILES: Methanol, Uraemia, Diabetic ketoacidosis, Propylene glycol, Isoniazid/Iron, Lactate, Ethylene glycol, Salicylates) are all potentially life-threatening and identifiable from three CMP values.
- Potassium < 3.0 or > 6.0 mmol/L — arrhythmia risk.
- Sodium < 125 or > 155 mmol/L — neurological risk.
- Glucose > 300 with ketones or symptoms — diabetic emergency.
- Calcium > 12 mg/dL — hypercalcaemia can cause confusion, arrhythmias.
- ALT/AST > 10× upper limit — severe hepatitis, drug reaction, ischaemic liver.
- Bicarbonate < 15 or an anion gap > 20 — acidosis workup.
CMP interpretation walk-through
- 1Any electrolyte critically abnormal?Address first — recheck immediately, review medications, correct fluid balance.
- 2Kidney panel abnormal?Assess acuity (compare to prior). Screen albumin-to-creatinine ratio, ultrasound if unexplained.
- 3Liver enzymes abnormal?Look at pattern (hepatocellular vs cholestatic), assess alcohol, hepatitis serology, ultrasound.
- 4Glucose abnormal?Confirm with fasting or HbA1c; investigate diabetes risk factors.
- 5Albumin low?Consider nutrition, chronic disease, protein-losing states (urine dip for proteinuria).
Related questions people ask
- What is the difference between a BMP and a CMP?
- How do I calculate the anion gap?
- When is potassium dangerous?
- What does a low albumin mean?
- How does dehydration change the CMP?
- What is high ALT with normal AST?
- How is eGFR calculated from creatinine?
Frequently asked questions
- The CMP is 14 numbers — patterns matter more than singletons.
- BUN-to-creatinine ratio, ALT-to-AST ratio, and albumin-corrected calcium are high-yield pairs.
- Anion gap = Na − (Cl + HCO₃); high anion gap acidosis is potentially life-threatening.
- Potassium below 3.0 or above 6.0 needs urgent attention.
- Sodium below 125 or above 155 needs urgent attention.
- ALT is the most liver-specific enzyme on the panel.
References
3 sources- AACCComprehensive Metabolic Panel
US laboratory medicine reference.
testing.com
- ACPChoosing Wisely: Chem-14 Testing
Guidance on appropriate ordering.
choosingwisely.org
- NICE CKSElectrolyte Disturbances
UK electrolyte management pathways.
cks.nice.org.uk
Evidence Snapshot
This snapshot shows verified evidence records matched to this article. It is not a diagnosis or personal medical advice.
A comprehensive metabolic panel is used as a broad screen of overall metabolic status, kidney and liver function and electrolyte balance, and is not designed to diagnose a specific single condition on its own.
Limitation. A comprehensive metabolic panel does not include cholesterol, thyroid tests or a complete blood count and therefore does not cover every routine screening domain.
A comprehensive metabolic panel (CMP) is a group of blood tests that typically includes measurements of glucose, calcium, electrolytes (sodium, potassium, chloride, bicarbonate), kidney tests (BUN and creatinine) and liver tests (albumin, total protein, ALP, AST, ALT and bilirubin).
Limitation. The exact list of analytes on a comprehensive metabolic panel can vary slightly between laboratories.
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