Why is CK used as the diagnostic marker for rhabdomyolysis instead of myoglobin?

• A. CK is easier to measure in the blood and serves as a marker of muscle damage; myoglobin is involved in the damage but is harder to measure.
• B. Myoglobin is less harmful than CK.
• C. CK directly causes kidney failure, unlike myoglobin.
• D. Myoglobin cannot be detected in the blood.

Answer: (A)

When diagnosing rhabdomyolysis, you want a blood marker that reliably reflects muscle injury and is easy to measure. Creatine kinase fits this well because it is released from damaged skeletal muscle and climbs in the blood, with standardized lab tests readily available. Its levels rise and remain elevated for a practical window, making it a stable indicator for diagnosis and monitoring.

Myoglobin does appear early after muscle damage, but it isn’t as dependable for several reasons. It’s cleared rapidly by the kidneys and has a short half-life, so its blood levels can fall quickly and be harder to interpret. Assays for myoglobin are less standardized and less routinely used, which can lead to variability in results. Because of these factors, relying on CK provides a clearer, more consistent picture of the extent of muscle injury.

CK is not a cause of kidney failure; kidney injury in rhabdomyolysis is multifactorial and related to circulating myoglobin among other factors, but that doesn’t make CK a better marker for injury. Myoglobin can be detected, but its measurement is less reliable for diagnosis than CK.