Serum creative kinase-3 (CK-3) is elevated in
**Core Concept**
Serum creatine kinase-3 (CK-3), a subtype of creatine kinase, is an enzyme that plays a crucial role in energy metabolism in skeletal muscle. Elevated levels of CK-3 can indicate muscle damage or disease.
**Why the Correct Answer is Right**
CK-3 is predominantly found in skeletal muscle, where it helps to catalyze the transfer of phosphate groups in the phosphocreatine kinase reaction. Elevated CK-3 levels are often associated with skeletal muscle injury or disease, such as rhabdomyolysis, muscular dystrophy, or intense exercise. This is because the muscle cell membrane is damaged, releasing the enzyme into the bloodstream.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because CK-3 is not typically associated with cardiac muscle damage, which would elevate CK-MB (creatine kinase-myocardial band) levels instead.
**Option B:** This option is incorrect because CK-3 is not a specific marker for liver disease; liver enzymes such as ALT and AST are more commonly associated with liver damage.
**Option C:** This option is incorrect because CK-3 is not a specific marker for renal disease; creatinine and urea levels are more commonly associated with kidney function.
**Clinical Pearl / High-Yield Fact**
Remember that CK-3 elevation is often seen in skeletal muscle injury, while CK-MB elevation is more specific to cardiac muscle damage.
**Correct Answer:** A. Skeletal muscle injury.