CK-MB

For the mass assay in ug/L; upper limits between 3.6 and 7 are printed depending on the method. Older reports give CK-MB as an activity in U/L or as a percentage of total CK, which are different scales.

Creatine kinase is an enzyme found in muscle, and the MB form is the version found mostly in heart muscle. When heart muscle is injured, CK-MB leaks into the blood and rises within a few hours. It has largely been replaced by troponin, which is more specific to the heart, but some laboratories still report it.

Doctors request it, sometimes alongside troponin, when looking for injury to the heart muscle, and occasionally to help tell heart muscle from skeletal muscle as the source of a raised total creatine kinase.

• A heart attack, rising within a few hours and falling over two to three days
• Inflammation of the heart muscle or injury during heart surgery
• Severe skeletal muscle injury or muscle disease, since skeletal muscle contains a small amount
• Very hard exercise
• Kidney disease, a little, because it is cleared more slowly

• Recovery after a heart injury; it returns to its resting level within two to three days
• Values near zero are usual in healthy adults; there is no lower limit
• It is a small fraction of the total creatine kinase, so most reports show single-figure values

• Strenuous exercise or a heavy fall in the days before
• A large skeletal muscle injury releases enough to raise it without any heart injury
• Methods differ between laboratories and old activity units are not comparable with mass units

No preparation needed. Timing in relation to the onset of symptoms matters, and doctors usually read it alongside troponin and total creatine kinase from the same sample.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.