In reviewing clinical chemistry profiles of two patients, P1 has increased CK and AST, P2 has increased CK. Which patient has acute muscle injury?

In reviewing clinical chemistry profiles of two patients, P1 has increased CK and AST, P2 has increased CK. Which patient has acute muscle injury?

• A. The patient with CK and AST elevated.
• B. The patient with CK elevated only.
• C. Both patients.
• D. Neither patient.

Answer: (B)

Acute skeletal muscle injury is most directly indicated by a rise in creatine kinase (CK) because CK-MM, the muscle-specific isoenzyme, leaks into the blood when muscle fibers are damaged. CK is a sensitive marker for muscle injury and rises promptly after injury, whereas AST is less specific. AST is present in both liver and muscle, so an elevated AST could reflect liver pathology in addition to muscle injury. When CK is elevated alone, the pattern points more specifically to acute muscle injury. If both CK and AST are elevated, it could still reflect muscle injury, but the AST elevation introduces ambiguity about a non-muscle source. Therefore, the patient with CK elevation only is the best indicator of acute muscle injury.

Acute skeletal muscle injury is most directly indicated by a rise in creatine kinase (CK) because CK-MM, the muscle-specific isoenzyme, leaks into the blood when muscle fibers are damaged. CK is a sensitive marker for muscle injury and rises promptly after injury, whereas AST is less specific. AST is present in both liver and muscle, so an elevated AST could reflect liver pathology in addition to muscle injury. When CK is elevated alone, the pattern points more specifically to acute muscle injury. If both CK and AST are elevated, it could still reflect muscle injury, but the AST elevation introduces ambiguity about a non-muscle source. Therefore, the patient with CK elevation only is the best indicator of acute muscle injury.