Technical Evaluation of Thyroid Assays on the Vitros ECi

Abstract

The Vitros ECiTM analyzer (Ortho Clinical Diagnostics, Rochester, NY) uses a new enhanced chemiluminescence technology. The assay reagents and wells are supplied together in combined packs with calibration information stored on magnetic calibration cards with bar-coded calibrators. We evaluated the following thyroid assays: thyrotropin (TSH), free thyroxine (fT4), free triiodothyronine (fT3), thyroxine (T4), and triiodothyronine (T3). Noteworthy is that the novel free thyroid hormone assay uses an alternative methodology to the frequently used one-step analog or two-step methodology. The conventional analog system uses a tracer-labeled T4 conjugate. The fT4 assay uses a peroxidase-labeled antibody to T4. We assessed 872 consecutive subjects from a healthy adult population for TSH and fT4, and smaller cohorts of 120 and 146 subjects for the total hormone and fT3 reference intervals, respectively. The subjects conformed to accepted criteria for establishment of a reference population (1). In addition, patients on regular follow-up with established thyroid disorders were also used in the technical evaluation of the assays. All procedures conformed to the Helsinki Declaration of 1975 and the 1996 revision. Reference intervals were established using rank and percentile confidence limits for euthyroid samples from a multiphasic screening program collected from the local population. The subjects presented with no evidence or clinical suspicion of thyroid abnormalities, including family history of thyroid disorders, pituitary disorders, and psychoses; were not on drugs known to interfere with thyroid gland metabolism or hormone assays; and their results for hepatic and renal function tests and complete blood counts were within the health-related reference intervals (1). Table 1⇓ shows the two-tailed 95th interpercentile reference intervals obtained from groups of euthyroid subjects. We measured TSH in 11 …