A 39-year-old male patient complains of moderate pain and weakness in the shoulder, back and pelvic girdle muscles, that has been progressing for the last 3 weeks; great difficulty in getting out of bed, going up and down the stairs, shaving. Dermatomyositis has been suspected. Blood test results: Hb-114 g/l, WBC- 10,8 - 109/l, eosinophils - 9%, ESR -22 mm/h, C-reactive protein - (++). The alteration in the following laboratory value wil be of decisive diagnostic significance: