GPT and myopathy: A partially validated laboratory test to assess the activity of myopathies is to assay the muscle enzymes: creatine kinase (CK), transaminase enzymes including aspartate transaminase (AST), and alanine transaminase (ALT) and aldolase A, an isomer present in muscles, other isomers (aldolase B and C) are present in brain or liver and are not found in plasma, except in liver diseases.