AUTOANTIBODIES TO TRIIODOTHYRONINE AND THYROXINE IN A GOLDEN RETRIEVER

A golden retriever presented with signs of hypothyroidism occurring in conjunction with autoantibodies to both triiodothyronine (T-3) and th yroxine (T-4) The autoantibodies caused the apparent concentrations of total T-3, total T-4 and free T-4 by analog assay to be high. However , free T-4 concentration was nondetectable when measured using a dialy sis assay. The dog's clinical condition markedly improved in response to L-thyroxine therapy and the free T-4 concentration by dialysis assa y increased into the normal range. Thyroid hormone autoantibodies can confuse the diagnostic evaluation for suspected hypothyroidism. In dog s with autoantibodies to T-4 measurement of free T-4 by dialysis assay is useful for both diagnostic and therapeutic monitoring purposes.