Creatine Kinase and Isoenzymes CK Study Notes in Plain Language

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Overview of Creatine Kinase

An enzyme that activates the conversion of creatine to ATP
Composed of two subunits, M and B, which combine to form three isoenzymes: CKMM, CKMB, and CKBB

Distribution of Isoenzymes

graph LR;
    A["Creatine Kinase CK"] --> B[CKBB];
    A --> C[CKMB];
    A --> D[CKMM];
    B --> sub1[Mainly found in brain, prostate, intestines, lungs, bladder, uterus, placenta, and thyroid];
    B --> sub2["CKMB is almost absent in normal human serum and can be neglected<br>If CKMB is higher than CK, it indicates a significant increase in CKBB being mistaken for CKMB"];
    C --> sub3["Mainly found in myocardial tissue<br>Myocardium: CKMM (70%), CKMB (30%)"];
    D --> sub4["Mainly found in skeletal muscle tissue<br>Skeletal muscle: CKMM (99%), CKMB (1%)"];

Clinical Significance

	Troponin+	Troponin-
CKMB+	Acute myocardial infarction is highly likely
CKMB-	1. Myocardial infarction has already occurred, but CKMB has not yet risen or has already declined after the time window 2. Small infarction area, CKMB elevation not obvious 3. Cause of myocardial injury to be determined (infection, heart failure, renal failure, etc.)	Basically not myocardial infarction

Activity Measurement

1. Total CK elevated
   1. CKMB increased, first consider myocardial injury, secondly possible skeletal muscle issues (skeletal muscle also contains some MB; intense exercise, skeletal muscle injury, muscle injection, CO poisoning can all cause MB elevation)
   2. CKMB/total CK increased (usually about 6%), generally indicates myocardial problems
2. Total CK not elevated
   1. CKMB/total CK increased, CKBB mistaken for CKMB, commonly seen in lung cancer

Quality Measurement

1. More expensive

Notes

Eating crayfish and intense exercise can both lead to CK elevation