Serum myoglobin level in altered thyroid states.

Serum myoglobin (Mb) levels were measured in normal, hyperthyroid, and hypothyroid subjects by RIA. Serum Mb levels were significantly higher (P less than 0.001) in untreated hypothyroid patients and significantly lower (P less than 0.01) in untreated hyperthyroid patients than in normal subjects. There was a significant inverse correlation (P less than 0.01) between serum T4 or T3 levels and Mb levels in these subjects. Serum Mb levels were normalized after correction of the abnormal thyroid states.