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

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).

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.

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.

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.