doiSerbia

Challenges in interpretation of thyroid hormone test results

Lalić Tijana (Clinical Center of Serbia, Clinic for Endocrinology, Diabetes and Metabolic Disorders, Belgrade)
Beleslin Biljana (Clinical Center of Serbia, Clinic for Endocrinology, Diabetes and Metabolic Disorders, Belgrade + School of Medicine, Belgrade)
Savić Slavica (Clinical Center of Serbia, Clinic for Endocrinology, Diabetes and Metabolic Disorders, Belgrade)
Stojković Mirjana (Clinical Center of Serbia, Clinic for Endocrinology, Diabetes and Metabolic Disorders, Belgrade)
Ćirić Jasmina (Clinical Center of Serbia, Clinic for Endocrinology, Diabetes and Metabolic Disorders, Belgrade + School of Medicine, Belgrade)
Žarković Miloš (Clinical Center of Serbia, Clinic for Endocrinology, Diabetes and Metabolic Disorders, Belgrade + School of Medicine, Belgrade)

Introduction. In interpreting thyroid hormones results it is preferable to think of interference and changes in concentration of their carrier proteins. Outline of Cases. We present two patients with discrepancy between the results of thyroid function tests and clinical status. The first case presents a 62-year-old patient with a nodular goiter and Hashimoto thyroiditis. Thyroid function test showed low thyroid-stimulating hormone (TSH) and normal to low fT4. By determining thyroid status (ТSH, T4, fT4, T3, fT3) in two laboratories, basal and after dilution, as well as thyroxine-binding globulin (TBG), it was concluded that the thyroid hormone levels were normal. The results were influenced by heterophile antibodies leading to a false lower TSH level and suspected secondary hypothyroidism. The second case, a 40-year-old patient, was examined and followed because of the variable size thyroid nodule and initially borderline elevated TSH, after which thyroid status showed low level of total thyroid hormones and normal TSH. Based on additional analysis it was concluded that low T4 and T3 were a result of low TBG. It is a hereditary genetic disorder with no clinical significance. Conclusion. Erroneous diagnosis of thyroid disorders and potentially harmful treatment could be avoided by proving the interference or TBG deficiency whenever there is a discrepancy between the thyroid function results and the clinical picture.

Keywords: thyroid hormone assays, interference, thyroid-binding globulin