Sospecha de la interferencia en la determinación de las hormonas tiroideas en la práctica clínica real

Introduction

Analytical methods providing plasma values of thyroid hormones are vulnerable to various interferences that alter the results. An example is the presence of anti-thyroid hormone antibodies (anti-HT), common in patients with autoimmune hypothyroidism, which can disrupt the instrument signal and yield a falsely elevated hormone value in the sample. Only 50% of cases of analytical interferences are reported. These interferences can lead to misdiagnoses and inappropriate therapeutic management, resulting in harm to the patient and increased healthcare expenditure.

Case

A 72-year-old woman with autoimmune hypothyroidism on replacement therapy. Routine analysis reveals an elevation in T4 with TSH also above the reference range, when the expected outcome would be TSH suppression. This pattern is confirmed twice with the same analyzer. As the patient is asymptomatic, analytical interference is suspected. Following a protocol established by the Clinical Analysis laboratory, major known interferences are ruled out, leading to the detection of anti-HT as the cause of the false T4 value. Management changes, with medication dosage now monitored solely based on TSH levels.

Conclusions

Interferences lead to erroneous interpretations. In this case, considering overdosing of treatment and reducing the LT4 dose would induce hypothyroidism symptoms. Assuming another form of hyperthyroidism, discontinuing treatment, or initiating anti-thyroid drugs would result in similar harm. By detecting the interference, unnecessary iatrogenesis is avoided.