Why is there more creatine kinase in dmd muscles compared to average muscles

Almost everyone with a neuromuscular disorder has had, or will have, a creatine kinase test. But what exactly is creatine kinase (CK), and why are its levels measured in neuromuscular diseases?

CK, also known as phosphocreatine kinase, or CPK, is a type of protein called an enzyme. It catalyzes, or "encourages," a biochemical reaction to occur. The normal function of CK in our cells is to add a phosphate group to creatine, turning it into the high-energy molecule phosphocreatine. Phosphocreatine is burned as a quick source of energy by our cells.

However, the normal function of CK isn't as relevant, in this case, as what happens to CK when muscle is damaged. During the process of muscle degeneration, muscle cells break open and their contents find their way into the bloodstream. Because most of the CK in the body normally exists in muscle, a rise in the amount of CK in the blood indicates that muscle damage has occurred, or is occurring.

To measure CK levels, a blood sample is taken and separated into fractions that contain cells and a fraction that doesn't - the serum. The amount of CK in the serum is reported in units (U) of enzyme activity per liter (L) of serum. In a healthy adult, the serum CK level varies with a number of factors (gender, race and activity), but normal range is 22 to 198 U/L (units per liter).

Higher amounts of serum CK can indicate muscle damage due to chronic disease or acute muscle injury. For this reason, if you're scheduled to have blood drawn for a CK test to diagnose a potential muscle disorder, you should limit your exercise to normal activities before the test.