Cardiac
CK-MB (creatine kinase MB isoenzyme)
CK-MB is the cardiac-enriched isoenzyme of creatine kinase, historically measured as a mass concentration to support the assessment of myocardial injury. At the point of care it is reported as a quantitative result within minutes, although cardiac troponin has now largely replaced it as the preferred marker for acute coronary syndrome.
Why it is measured
CK-MB is enriched in cardiac muscle, so a rise can reflect myocardial damage, and its relatively short half-life means it falls and rises again sooner than troponin. That property gives it a narrow residual role, for example in estimating infarct size or helping flag possible reinfarction soon after an index event.
| Typical range | Indicative adult mass assay: roughly 0 to 5 ng/mL (equivalent to µg/L), with sex-specific 99th-percentile cut-offs that are typically higher in men than in women. A CK-MB to total CK relative index (often expressed as a percentage) may also be calculated by some laboratories. Quantitative point-of-care cartridges report across a wide measuring interval (for example up to about 150 ng/mL). Cut-offs and reference intervals vary by method and analyser, so always apply the issuing laboratory's or device's own range. |
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| Sample | Sample type varies by platform, so always follow the specific device instructions. Quantitative point-of-care cartridges and reader-based immunoassays typically use a small volume of anticoagulated whole blood or plasma: for example lithium-heparin whole blood or plasma on the Abbott i-STAT, and EDTA whole blood on some fluorescence readers. Other reader assays and laboratory mass assays use serum or plasma, and lateral-flow cassette tests may accept whole blood, serum or plasma. |
| Turnaround | Typically a few minutes to about 15 minutes at the point of care, depending on platform: quantitative cartridge and reader systems give a result in minutes, while qualitative cassettes are usually read at around 10 to 15 minutes. |
Point of care devices that report it
- Abbott i-STAT CK-MB cartridge (quantitative mass assay, whole blood or plasma)
- Response Biomedical RAMP CK-MB test (quantitative fluorescence immunoassay reader, EDTA whole blood)
- Xiamen Biotime CK-MB rapid quantitative test (immunofluorescence analyser, serum or plasma)
- nal von minden NADAL CK-MB test cassette (qualitative lateral-flow immunoassay)
Questions, answered
If we already measure cardiac troponin, is CK-MB still useful?
For routine diagnosis of acute coronary syndrome, major cardiology guidelines now favour cardiac troponin because it is more sensitive and specific for myocardial injury, and many services have stopped ordering CK-MB alongside it. CK-MB retains only a narrow educational and operational role, for example estimating infarct size or supporting assessment of possible reinfarction soon after an index event, or where troponin is unavailable. Local protocols should define when, if ever, it is requested.
What sample does a point-of-care CK-MB test need?
It depends on the platform, so always follow the specific device instructions for anticoagulant type, fill volume and timing. Quantitative cartridge and reader systems typically take a small volume of anticoagulated whole blood or plasma applied directly to the device, with the required anticoagulant (for example lithium heparin or EDTA) set by the manufacturer, while other reader assays, laboratory methods and some cassette tests use serum or plasma. Using the wrong tube or an under-filled sample can invalidate the result.
Can CK-MB be raised without a heart attack?
Yes. CK-MB is found mainly in cardiac muscle but is also present in skeletal muscle, so elevations can follow strenuous exercise, skeletal muscle injury, surgery, myopathies or rhabdomyolysis, among other causes. Results are interpreted in clinical context and against the relevant cut-off by the responsible clinician, and this record does not provide patient-specific interpretation.