Endocrine Abstracts

Background: heterophilic antibodies are antibodies in patients’ sample that can cause false results by binding to the assay antibodies. Interference due to heterophilic antibodies may lead to falsely low or high analytic concentrations. In some settings, the relationship between TSH and thyroid hormones does not fit with the expected feedback mechanisms. This may be due to a pathophysiological process, laboratory error or assay interference.

Case report: A 37-year-old female patient diagnosed with primary autoimmune hypothyroidism since she was 16 years old, well controlled until 2016 when, in relation to a traffic accident with traumatic brain injury, she began with a discordant thyroid hormonal pattern consisting of high TSH levels with normal FT4 or TSH inadequately normal with high FT4, accompanied by symptoms of hyperthyroidism, especially tachycardia, fatigue and weight loss (Table 1) After several check-ups and verifying an abnormal pattern in thyroid function, requiring multiple changes in dose and presentation of levothyroxine, a study of secondary hyperthyroidism and poor absorption was decided; both results were negative. Given the lack of improvement, analysis without interference from heterophilic antibodies was finally performed in an external laboratory since it was not available in our center, the results demonstrates that presence of heterophilic antibodies, presenting adequate levels of TSH and FT4 after their neutralization (Table 2) Currently, the patient maintains follow-up in our clinic with dose adjustment according to analysis carried out without interference from heterophilic antibodies, presenting a significant symptomatic improvement after stabilization of the levothyroxine dose.

Conclusions: Interference in immunoassays is an important clinical problem that is underestimated and can have important clinical consequences. It is important to recognize the possibility of such interferences early in the diagnostic process and to implement protocols to identify these whenever possible, in a timely fashion, to prevent untoward consequences.