A 42 year old man with bilateral exophthalmos and weight loss

We thank Mathews and Syeed for their comments regarding thyroid stimulating hormone receptor antibody (TSH-RAb) testing. We agree, as stated in the article, that measurement of TSH-RAb is a useful test in helping to determine the cause of hyperthyroidism when there is doubt; due to space limitations we did not include a more detailed discussion of this issue. As the assay becomes more widely available, clinicians should be familiar and make use of this test when clinically indicated.