Enzymes within the body’s cells increase the rate at which life-sustaining chemical reactions occur. The cells of the various body tissues contain characteristic enzymes. When a particular tissue is injured or destroyed, its cells leak enzymes into the bloodstream. Elevated muscle enzymes in the blood indicate muscle tissue damage.
Role of Enzymes
Enzymes are proteins that serve as biological catalysts, according to author Geoffrey M. Cooper. In his book "The Cell, A Molecular Approach", Cooper explains that a catalyst speeds up the rate of a chemical reaction without being altered or consumed by the process. Biochemical reactions that take place within the body’s cells sustain life. Each of the thousands of enzymes in the body participates in a specific chemical reaction. Some enzymes break molecules apart; others join them together. Without enzymes, such reactions would occur too slowly to make life possible.
Muscle tissue cells contain characteristic enzymes including aldolase, creatine phosphokinase (CPK or CK), lactic dehydrogenase (LDH), glutamic-oxaloacetic transaminase (GOT), and glutamic-pyruvic transaminase (GPT). According to Medline Plus, aldolase is present in high amounts in muscle tissue to help break down sugars to produce energy. CPK is another enzyme that, according to the Myositis Association, is found primarily in muscle cells and facilitates energy production. In addition to their presence in muscle tissue, LDH, GOT, and GPT are also found in the tissues of other body organs such as the liver, pancreas, and kidneys and are less specific indicators of muscle damage.
Role of Testing
Muscle enzyme tests help physicians determine the cause of muscular symptoms such as pain and weakness. Muscle weakness can be a symptom of either a neurological disorder or a muscular disorder. According to the Myositis Association, muscle enzymes remain within normal range when weakness results from a neurological condition. Elevated muscle enzymes indicate disease of muscular origin. Muscle enzyme levels also help physicians determine damage severity and treatment effectiveness.
According to the Johns Hopkins Arthritis Center, muscle enzyme elevations can be caused by any process or disease that injures muscle tissue. This includes strenuous exercise, trauma, inflammation and medications. Muscle inflammation is called myositis, a common term used to describe a number of inflammatory muscle disorders including dermatomyositis, inclusion-body myositis, juvenile myositis, and polymyositis. Although the precise cause of inflammatory muscle disorders, or myopathies, is unknown, the Myositis Association claims they are thought to be autoimmune diseases. Autoimmune disease results when infection-fighting components in the body go awry and attack normal healthy tissues. Medications, particularly statin drugs used to lower cholesterol, may also cause abnormally high enzyme levels. According to the Johns Hopkins Arthritis Center, statin-induced myositis is a direct toxic effect of the drugs on muscle cells and resolves when the medications are discontinued.
Prolonged muscle weakness or pain requires medical evaluation. Blood tests to determine muscle enzyme levels aid in diagnosis only if the results are accurate. Properly preparing for muscle enzyme blood tests helps provide accurate results. The Myositis Association recommends limiting exercise to normal activities before the tests and informing the healthcare provider of any prescription or nonprescription medications being taken, as they may interfere with test results. Discontinue medications only if directed to do so by a healthcare professional.
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