Erythrocyte creatine levels in hyperthyroidism.

The mechanism by which erythrocyte mean corpuscular volume (MCV) is decreased in hyperthyroidism is not known. One possible mechanism is premature aging of erythrocytes in the circulation. Since erythrocyte creatine has been shown to be a good marker of cell senescence, we determined this in hyperthyroid patients and control subjects to examine whether the decrease in MCV is related to senescence. Erythrocyte creatine levels were similar in both hyperthyroid patients and controls, suggesting that premature senescence of erythrocytes does not account for the lower MCV in hyperthyroidism.