The document compares measurements of thyroid stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) using Luminescent Oxygen Channeling Immunoassay (LOCI) technology to routine assays. Method comparisons showed good agreement between LOCI and routine TSH assays but significant differences for FT4 and FT3 measurements. Reference intervals were established for the LOCI assays based on a study of 80 healthy individuals. Preliminary results demonstrate the potential of LOCI technology but also indicate a need for further evaluation of inter-assay differences and potential interference susceptibility.

1. Measurement of TSH, FT4 and FT3 with LOCI® Technology Verdickt L. 1 , Lepoutre T. 1 , Gruson D. 1 1 - Department of Laboratory Medicine, Cliniques universitaires St-Luc, Brussels, Belgium Email: verdicktl@gmail.com 2011 Biochimie Biochemistry Poster 21

2. Background Measurements of Thyroid Stimulating Hormone (TSH), free tetraiodothyronin (FT4) and triiodothyronin (FT3) are essential to achieve a complete assessment of thyroid function. Several immunoassays for the measurement of thyroid function parameters are available. (Mindy L. Rawlings and William L. Roberts, Performance Characteristics of Six Third Generation Assays for Thyroid Stimulating Hormone. Clinical Chemistry 50:12 2338 2344 (2004)) Homogenous immunoassays based on Luminescent Oxygen Channeling Immunoassays (LOCI®) have recently been developed for the measurement of TSH, FT4 and FT3 . (Ullman EF, KirakossianH Luminescent oxygen channeling assay (LOCI): sensitive, broadly applicable homogeneous immunoassay method. Clin Chem. 1996 Sep; 42 (9): 1518-26)

3. Objective To c ompar e LOCI® assays with our routine assays 40 samples were passed on the DXI® assays (Beckman Coulter) in the routine and then passed on the Dimension Vista® (Siemens) 2) To de termin e the reference values for LOCI® TSH, FT4 and FT3 assays We passed 80 healthy individuals to determine reference intervals on the Dimension Vista® (22women and 58men aged between 33 and 63years)

4. Results: method comparison TSH Vista (µUI/ml) TSH DXI (µUI/ml) Average of TSH Vista and TSH DXI (µUI/ml) TSH Vista – TSH DXI (µUI/ml)/ average y = - 0,041 + 1,028 x P > 0,05 (no deviation from the linearity) TSH 0 1 2 3 4 4,0 3,5 3,0 2,5 2,0 1,5 1,0 0,5 0,0 DxI Vista

5. Results: method comparison Average of FT4 Vista and FT4 DXI (ng/dl) FT4 Vista – FT4 DXI (ng/dl) / average FT4 DXI (ng/dl) FT4 Vista (ng/dl) y = - 0,07 + 1,653 x P > 0,10 (no deviation from the linearity) FT4

6. Results: method comparison FT3 Vista (pgI/ml) FT3 DXI (pg/ml) Average of FT3 Vista and FT3 DXI (pg/ml) FT3 Vista – FT3 DXI (pg/ml) / average y = -1,658 + 1,924 x P > 0,10 (no deviation from the linearity) FT3

7. Kolmogorov-Smirnov test for normal distribution accept normality (P= 0,771) ; N= 79 Kolmogorov-Smirnov test for normal distribution accept normality (P= 0,471) ; N= 79 Kolmogorov-Smirnov test for normal distribution accept normality (P= 0,992); N= 79 Results: reference values TSH: reference interval: 0,028-2,877μU/ml FT4: reference interval: 0,767 – 1,259ng/dl FT3: reference interval: 2,5- 3,953pg/ml

8. Discussion Our preliminary study has demonstrated a good agreement between LOCI® TSH assays and the comparative method. However, the method comparison study has underscored significant differences for LOCI® measurements for FT4 and FT3. Such differences can be related to immunoassays format. The susceptibility of LOCI® assays to potential interferences remains to be documented.