324 TRI-IODOTHYRONINE (T3) ELEVATION DUE TO DESICCATED THYROID

Fourteen hypothyroid children, 10 girls and 4 boys, had serum T4, T3 and TSH measured while receiving replacement therapy with desiccated thyroid and 6 weeks after beginning replacement therapy with sodium-l-thyroxine, 4.2±0.6(SD) μg/Kg per day (maximum 200 μg). Serum T3 while receiving desiccated thyroid was 393±144(SD) ng/dl compared to 157±23(SD) ng/dl while receiving thyroxine (P 0.1). Our findings show that a paradoxically elevated serum T3 concentration, unassociated with clinical hyperthyroidism is, in general, characteristic of treatment with desiccated thyroid. Replacement with sodium-l-thyroxine leads to normalization of all routine tests of thyroid function.