Unit Converter
CK‐MB mass – the MB isoenzyme of creatine kinase (quantitative determination)
(Creatine Kinase MB Isoenzyme – Quantitative Cardiac Marker)
Synonyms
- CK-MB (mass)
- Creatine kinase MB isoenzyme
- CK-MB protein concentration
- CK-2 isoenzyme
- Cardiac-specific CK isoenzyme
(Note: CK-MB mass is preferred over CK-MB activity due to higher specificity.)
Units of Measurement
- ng/mL
- ng/dL
- ng/100 mL
- ng%
- ng/L
- µg/L
1 ng/mL = 1 µg/L
ng/dL = ng/100 mL = ng%
Description
CK-MB (Creatine Kinase–MB isoenzyme) is an enzyme found primarily in cardiac muscle and in smaller amounts in skeletal muscle.
CK-MB mass concentration is the preferred CK-MB test for diagnosing and monitoring acute myocardial infarction (AMI) because it is:
- More specific than total CK
- More sensitive than CK-MB activity assays
- Less influenced by hemolysis or kidney disease
Despite troponins being the gold standard, CK-MB mass remains clinically useful in:
- Reinfarction
- Early MI detection (before troponin rises)
- Settings where troponin assays are unavailable or confounded
Physiological Role
CK-MB catalyzes:
Creatine phosphate+ADP↔Creatine+ATP\text{Creatine phosphate} + \text{ADP} \leftrightarrow \text{Creatine} + \text{ATP}Creatine phosphate+ADP↔Creatine+ATP
High energy turnover in cardiac muscle makes CK-MB a sensitive indicator of cardiomyocyte damage.
Clinical Significance
Elevated CK-MB
1. Acute Myocardial Infarction (Primary Use)
CK-MB kinetics:
- Rises: 3-6 hours after symptom onset
- Peaks: 12-24 hours
- Returns to normal: 48–72 hours
Useful for:
- Early MI diagnosis
- Detecting reinfarction (second peak)
- Monitoring reperfusion
2. Myocardial Injury (Non-MI)
Moderate elevation can occur in:
- Myocarditis
- Cardiac surgery
- Ablation procedures
- Defibrillation
- Severe tachyarrhythmias
3. Skeletal Muscle Injury
CK-MB can rise mildly because skeletal muscle contains ~1–3% MB fraction:
- Trauma
- Rhabdomyolysis
- Strenuous exercise
4. Renal Failure
Reduced clearance may elevate CK-MB.
Low or Normal CK-MB
Normal levels do not exclude MI once troponin assays are used (troponin is more sensitive).
Normal CK-MB is expected in healthy individuals.
Reference Intervals
(Tietz 8E + ACC/AHA + Mayo + ARUP + IFCC)
Typical Adult Reference Range
- < 5 ng/mL
or - < 5 µg/L
(Ranges vary slightly depending on assay manufacturer.)
Diagnostic Threshold for MI
- > 5–10 ng/mL depending on assay
- Or CK-MB relative index:
CK-MB Index=CK-MB (ng/mL)Total CK (U/L)×100\text{CK-MB Index} = \frac{\text{CK-MB (ng/mL)}}{\text{Total CK (U/L)}} \times 100CK-MB Index=Total CK (U/L)CK-MB (ng/mL)×100
>2.5–3% strongly suggests cardiac origin.
Reinfarction Criteria
- >10–20% increase from previous CK-MB value within 6–12 hours.
Unit Meanings
| Unit | Meaning |
| ng/mL | nanogram per milliliter |
| ng/dL | nanogram per deciliter |
| ng/100 mL = ng% | identical to ng/dL |
| ng/L | nanogram per liter |
| µg/L | microgram per liter |
Diagnostic Uses
1. Acute Myocardial Infarction
Helpful for:
- Early MI detection
- Reinfarction monitoring
- Distinguishing cardiac vs non-cardiac CK elevations
2. Post-Cardiac Procedures
Monitor injury after:
- CABG
- PCI
- RF ablation
- Valve surgery
3. Differential Diagnosis of Chest Pain
Along with:
- Troponin I/T
- ECG
- Clinical symptoms
4. Assessment of Reperfusion
Rapid fall in CK-MB suggests successful reperfusion therapy.
5. CK-MB Index
Used to differentiate:
- Cardiac source vs skeletal muscle injury
Analytical Notes
- Immunoassay-based (high specificity for MB subunit)
- Hemolysis: minimal effect
- Macro-CK can interfere (rare)
- Serial testing improves accuracy
- Troponins remain preferred but CK-MB still useful in select scenarios
Clinical Pearls
- CK-MB is excellent for detecting reinfarction because it normalizes quickly (48–72h), unlike troponins.
- Relative index >2.5–3% → likely cardiac injury even if total CK is high.
- In chronic renal failure, CK-MB may be mildly elevated; interpret with caution.
- Exercise can increase CK but not CK-MB significantly.
- Troponins are more sensitive, but CK-MB is still valuable in early MI and procedural myocardial injury.
Interesting Fact
Before troponins, CK-MB was the gold standard for diagnosing myocardial infarction. It remains one of the earliest cardiac biomarkers incorporated into emergency medicine.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Cardiac Markers.
- ACC/AHA Guidelines for Acute MI.
- IFCC Standards for CK Isoenzyme Measurement.
- Mayo Clinic Laboratories - CK-MB.
- ARUP Consult - Cardiac Biomarkers.