An investigation into creatine kinase and other plasma enzymes in thyroid disorders.

The relationship between plasma protein bound iodine (PBI) level and creatine kinase (CK) activity was investigated in 143 males and 528 females suspected of various thyroid disorders; there was significant negative correlation between low PBI level and raised CK activity. CK, aldolase, lactate dehydrogenase (LD), aspartate transaminase (AST), and alanine transaminase (ALT) activities were determined in plasma from patients with reduced PBI levels; apart from CK, LD was the only enzyme increased in an appreciable number of cases. A further series of specimens was collected from 66 patients with low PBI levels and the CK isoenzymes investigated. In all of these MM was the main form present; a trace of MB was found in 6. These findings do not explain the elevation of CK in hypothyroidism which may be a non-specific effect.