Serum Creatine Phosphokinase Activity in Altered Thyroid States

Serum creatine phosphokinase activity was determined in euthyroid, hyperthyroid and hypothyroid subjects. Mean serum enzyme values (μmol substrate converted/ml/hr) were: 2.03 (±0.216) for healthy subjects, 1.71 (±0.257) for euthyroid patients, 0.72 (±0.08) for hyperthyroid patients and 13.22 (±3.22) for hypothyroid patients. Serial studies in hyper- and hypothyroidism demonstrated good correlation of serum enzyme activity with thyroid function. The assay of this enzyme was found to be useful in the assessment of thyroid status in patients who received exogenous iodine or diphenylhydantoin. Concurrent injury or inflammatory disease of skeletal or cardiac muscle invalidates the diagnostic value of CPK in hypothyroidism but increases its usefulness in hyperthyroidism.