Evaluation of LOCI technology-based thyroid blood tests on the Dimension Vista analyzer.

Objectives: To assess the performance of thyroid-stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyronine (FT3) determinations by luminescent oxygen channeling immunoassay (LOCI) technology on the Dimension Vista analyzer (Siemens Healthcare Diagnostics).

Design & Methods: We assessed 1) functional sensitivity for TSH (FSe-TSH), and intra- and inter-assay variations for TSH, FT4 and FT3 on Vista; 2) comparisons of serum and heparin-treated plasma on Vista; 3) comparisons of a) plasma TSH by Vista versus electrochemiluminescence (ECLIA) on Roche Modular analyzer, and b) plasma FT4 and FT3 by Vista versus Immunotech-Beckman radioimmunoassay (RIA); and 4) association of albumin and prealbumin levels with free thyroid hormone concentrations on Vista.

Results: 1) FSe-TSH concentration was below 0.005 mIU/L. Maximum intra-assay CVs (2.1%, 1.4%, 5.2%) and inter-assay CVs (16.5%, 5.1%, 5.8%) were good for TSH, FT4 and FT3 respectively. 2) Heparin-treated plasma samples consistently gave slightly higher values than serum for TSH, FT4 and FT3. 3) Passing-Bablok regression gave: TSH: [LOCI]=0.91[ECLIA]-0.08 (concordance correlation coefficient ρ(c)=0.95); FT4: [LOCI]=1.05[RIA]-1.55 (ρ(c)=0.80); and FT3: [LOCI]=1.05[RIA]-0.06 (ρ(c)=0.81). 4) Both serum albumin and prealbumin concentrations were positively associated with FT3 levels and negatively associated with FT4 levels in patients.

Conclusion: LOCI is accurate for TSH, FT4 and FT3 analysis. Despite a slight significant bias compared to ECLIA, LOCI is precise for TSH and fulfills the third-generation criteria. However, the poor concordance between LOCI and RIA for FT4 and FT3, and the dependence of these hormones on binding proteins require further investigation.