Diagnosis of Myositis
Creatine kinase is the most specific blood test - 5-50 times above the reference level. A level greater than 100 times the reference level is rare and is a signal of other diagnoses.
Muscle biopsy - Medscape Reference
Aldolase
Erythrocyte sedimentation rate (esr) often elevated.
Myoglobinuria may be present.
Positive rheumatoid factor in more than 50% of patients.
Positive antinuclear antibody results in less than 50% of patients.
Leukocytosis is present in more than 50% of patients
Diagnostic Criteria for Polymyositis/Dermatomyositis at The Myositis Association
Diagnostic Criteria for Inclusion Body Myositis at The Myositis Association
Diagnostic Criteria for Juvenile Dermatomyositis at The Myositis Association