Serum Level of Biotin Rather than the Daily Dosage Is the Main Determinant of Interference on Thyroid Function Assays.

Introduction: Several case reports stress that high-dose biotin causes incorrect laboratory results. However, the extent of this interference in children is not systematically studied. Aim: To assess factors associated with biotin interference on thyroid function tests in subjects with biotinidase deficiency. Method: The study included 44 children who were treated with oral biotin (Group 1, median dose: 10 mg/day [25–75p; 10–10], age: 1.83 years [1.04–2.90]) and 30 healthy subjects (Group 2, age: 1.05 years [0.37–3.37]). Thyroid function tests were performed with two different assays, and streptavidin-coated particles were used in order to remove biotin from serum samples of cases with biotin interference. Results: The measurements were first performed with Beckman Coulter. In Group 1, remarkably high levels of fT3 and fT4 were found in 26 (59.1%) and 25 (56.8%) patients, respectively. Thyroid hormone functions were all normal in Group 2. Significantly higher serum biotin levels were detected in interference-positive children (p < 0.001). The serum biotin levels in Group 1 showed a strong positive correlation with fT3 (r = 0.867, p < 0.001) and fT4 levels (r = 0.905, p < 0.001). A serum biotin level of 80.35 µg/L was found to be the best cut-off value for predicting interference (sensitivity: 96.2% and specificity: 94.4%). When analyzed with Siemens Advia Centaur XP, all thyroid function tests were normal in both groups except in one patient (2.27%) with slightly elevated fT3 level in Group 1. Repeated tests with Beckman Coulter after neutralization of biotin with streptavidin magnetic particles in serum samples of the interference-positive cases revealed normal thyroid hormone levels. Conclusion: Interference is an important problem in thyroid function tests in nearly 60% of all children receiving biotin treatment for biotinidase deficiency. Serum levels of biotin rather than the dosage are the main determinant of interference, which can be eliminated by choosing appropriate laboratory methods.