Creatine Kinase is an important chemical in muscle fibres and there is normally a small amount of it in the blood serum. In DMD and BMD, creatine kinase leaks out of the muscle fibres and is therefore found in greatly increased amounts in the serum. In young boys with DMD, the SCK level is nearly always at least 5 times as high as the maximum for unaffected people. It is sometimes 50 to 100 times as high. The diagnosis should be confirmed by muscle biopsy.
Muscle biopsy involves the removal of a small piece of muscle for examination.
Since the discovery of the defect of dystrophin in DMD it has also been possible to arrange for muscle biopsy specimens to be examined for this specific defect. The worsening of disability can be slowed by such measures as physiotherapy, but it cannot be stopped. On average, use of a wheelchair proceeds from occasional use at about age 9 years to almost total dependence by the early teens, but there is a range of severity to either side of this. As the ability to walk is lost, the function of the hands and arms becomes increasingly important in determining the affected person's abilities. Most affected people survive into their twenties.