We have recently reported that red blood cell (RBC)
zinc (Zn) in patients with
hyperthyroidism reflects a patient's integrated
thyroid hormone level over the previous few months. In the present paper RBC Zn concentrations were measured in 10 patients with
subacute thyroiditis whose total plasma T4 and T3 levels were elevated. The values were compared with those obtained in 10 patients with untreated
Graves' disease, whose plasma T4 concentrations were elevated to the same level as in the former group. The RBC Zn concentration was normal in 9 of 10 patients with
subacute thyroiditis, but was depressed in all patients with
Graves' disease. The mean (+/- SE) RBC Zn in patients with
subacute thyroiditis was 162 +/- 9 mumol/L, significantly (P less than 0.001) higher than that in
Graves' disease (87 +/- 5 mumol/L). During
prednisolone treatment the RBC Zn in patients with
subacute thyroiditis remained at the normal level and did not change significantly, although it was slightly decreased at 2 and 4 weeks of treatment. On the other hand, the RBC Zn in patients with
Graves' disease was significantly increased at 8 weeks of treatment and reached the normal range in 12 weeks. These results suggest that elevation of plasma
thyroid hormone concentrations in patients with
subacute thyroiditis is transient and does not cause any significant change in the RBC Zn concentration.