ESPE Abstracts

Introduction: Differential diagnosis of thyroid hormone resistance (beta) and TSHoma should be made in patients with high free thyroxine (f-T4) and free triiodothyronine (f-T3) and non-suppressed thyroid stimulating hormone (TSH) levels. The aim of this study was to present the results of etiological research in a patient with Down syndrome who was clinically euthyroid and had high levels of f-T4, f-T3, normal TSH levels.

Case: A 28-day-old male patient with Down syndrome was referred our hospital becouse of high f-T4 levels from another state hospital.

Background: It was learned that the patient was born 3270 g, operated for pediatric surgery for hirschsprung disease and used biotin at a dose of 10 mg / day due to biotinidase deficiency.

Family history: Parents had no known thyroid dysfunction.

Physical Examination: Weight 4020 gr (-0.68 SDS), Length 52 cm (-0.55 SDS), Head circumference: 38 cm (0.07 SDS), Pulse: 130 / min, Blood pressure: 90/50 mmHg, the anterior fontanel was 1.5x1 cm, the thyroid was non-palpable, the other system examinations were normal, other than the Down syndrome stigmatics.

Laboratory: fT3: 14.9 ng / dl (2.5-4.4), fT4: 4.08 ng / dl (0.54-1.24), TSH: 2.65 mU / L (0.34-5.6), After 1 week of repeated tests in the same laboratory; fT3: 14.3 ng / dl (2.5-4.4), fT4: 3.69 ng / dl (0.54-1.24), TSH: 2.88 mU / L (0.34-5.6).

Clinical follow-up: As the patient was clinically euthyroid and had a history of biotin use, the method of TFT was investigated with biotin interference. The patient's sT3 and sT4 tests were found to be studied in an immunoassay system (DxI, Beckman Coulter Inc., USA) using streptavidin-biotin and interfering with it. There was no interference in the same tests on a different immunassay platform (Architect 2000, Abbott Lab., USA) which did not use this pairing methodically. fT3: 3.64 pg / ml (1.5-6.4) fT4: 1.17 ng / ml (0.48-2.34) TSH: 2.53 uIU / ml (0.62-8) was normal.

Conclusion: Biotin-streptavidin interaction is the most potent non-covalent interaction in nature and is frequently used in immunoassay measurements. The direction and magnitude of the biotin interfarans may vary depending on the immunoassay platform and test run. In particular, the use of high-dose biotin may result in erroneous results depending on the principle of the test (competing or sandwich). It is an appropriate approach to repeat the analyzes in alternative immunassay platforms in cases where interference is suspected.