Endocrine Abstracts

Background: Measurements of TSH, free tetraiodothyronin (FT₄) and triiodothyronin (FT₃) are essential to achieve assessment of thyroid function. Luminescent Oxygen Channelling Immunoassays (LOCI) have recently been developed for the measurement of biomarkers of thyroid function. Such homogeneous immunoassays allow a faster delivery of the results. The aim of our study were therefore to determine the reference values for LOCI TSH, FT₄ and FT₃ assays and to compare LOCI assays with our routine assays.

Method: Serum samples from 129 healthy individuals (mean age: 54 years, 45 females and 84 males) were evaluated with the LOCI TSH, FT₄ and FT₃ assays on the Dimension Vista (Siemens). In addition, patients’ samples from our laboratory routine flow (n=177) were used for method comparison with the DxI assays (Beckman Coulter), a ‘conventional’ heterogenous immunoassay.

Results: The reference intervals obtained from the healthy volunteers group were for LOCI assays: .27–2.89 μU/ml for TSH, 0.80–1.30 ng/dl for FT₄ and 2.61–4.06 pg/ml for FT₃. The LOCI assays were significantly correlated with our routine assays (r=0.987, P<0.0001 for TSH; r=0.924, P<0.0001 for FT₄ and r=0.514, P<0.0001 for FT₃). For the method comparison, the Passing and Bablok regression analysis showed intercepts of −0.015; 0.098 and 0.297 for TSH, FT₄ and FT₃ respectively. The slopes were 1.107 for TSH, 1.333 for FT₄ and 1.075 for FT₃. No significant deviation from linearity for these three parameters was observed. Bland and Altman plots revealed mean differences of −1.8 for TSH, 0.36 for FT₄ and 0.47 for FT₃.

Conclusion: Our study has provided reference values for the LOCI TSH, FT₄ and FT₃ assays. Furthermore, we have demonstrated a good agreement between LOCI assays and ‘conventional’ immunoassays.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.