avoiding misdiagnosis due to antibody interference with serum free thyroxin

Introduction: interfering antibodies are capable of causing potentially misleading results in automated thyroid hormone immunoassays. case presentation: we report the case of a 46-year-old female patient with autoimmune hypothyroidism in chronic replacement treatment with levothyroxine who was presented 8 years after diagnosis with a thyroid function test showing an increased level of tsh and a very high level of ft4. interference in the laboratory serum free thyroxin (ft4) test was suspected, due to the lack of symptoms of hyperthyroidism and a different immunoassay platform confirmed a low ft4 result. the discrepancy between the two results was explained by the presence of antit4autoantibodies. conclusions: antibody interference with serum free thyroxine must be considered when clinical findings and laboratory results show discrepancies.