Caution, however, should be exercised in interpreting thyroglobulin results without thyroglobulin antibodies, since thyroglobulin antibodies commonly interfere in thyroglobulin immunoassays causing false positive and negative results which may lead to clinical misdirection. In such cases, increased faecal thyroxine levels in thyrotoxicosis factitia may help differentiate it from other causes of hyperthyroidism.