ESPE Abstracts

Introduction: High doses of biotin are reported to cause incorrect results in various immunoassays in some patients. However, there is no systematic study regarding biotin interference in childhood.

Aim: To assess thyroid function with different methods in subjects with biotinidase deficiency, to determine the factors causing interference, and to investigate the efficiency of the methods for overcoming interference.

Method: The study included children with biotinidase deficiency who were regularly treated with biotin [Group 1, n=44, female/male: 26/18, median dose: 10 mg/day (25–75p; 10–10), age: 1.83 years (1.04–2.90)] and healthy subjects [Group 2, n=30, female/male: 16/14, age: 1.05 years (0.37–3.37)]. Blood samples in Group 1 were obtained two hours after the morning biotin dose. Serum fT3, fT4, and TSH levels were measured using both biotin-containing (Beckman Coulter) and biotin-free methods (Siemens Advia Centaur XP). Serum biotin levels were measured (in duplicate) with an ELISA-based kit. Streptavidin coated particles were used to remove biotin for serum samples of cases with biotin interference.

Results: Age, gender, weight, and height were similar between two groups. The measurements were first performed with Beckman Coulter. In Group1, TSH levels were normal in all of the cases but 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. The clinical features including biotin doses were similar (P=0.955) between interference-positive (Group 1A, n=26) and remaining (Group 1B, n=18) patients except significantly higher serum biotin levels Group 1A [221 μg/L (145–349) vs. 49 μg/L (38–71), P <0.001]. Serum biotin levels in Group 1 showed a strong positive correlation with fT3 (r=0.867) and fT4 levels (r=0.905). The serum biotin level of 80.35 μg/L was found to be the best cut-off value for predicting interference (96.2% sensitivity and 94.4% specificity) with a discriminative ability of 0.987±0.01, P<0.001 (95% CI: 0.962–1.000). When analyzed with Siemens Advia Centaur XP, all thyroid function tests were normal in both groups except one patient (2.27%) with high fT3 level in Group 1. Repeated tests with Beckman Coulter after neutralization of biotin with streptavidin magnetic particles in serum samples of the cases in Group1A revealed no interference.

Conclusion: Interference is an important problem in thyroid function tests in children receiving biotin treatment for biotinidase deficiency. Serum levels of biotin rather than the dose are the main determinant of interference, which can be eliminated by choosing appropriate laboratory methods.