A-032 Evaluation of the Analytical Performance of Total Triiodothyronine (T3) and Total Thyroxine (T4) Assays on the Atellica CI Analyzer

Abstract Background Primary malfunction of the thyroid gland may result in excessive or below normal release of Total Triiodothyronine (T3) or Total Thyroxine (T4). Since thyroid function is directly affected by thyroid stimulating hormone, malfunction of the pituitary or the hypothalamus may influence circulating blood levels of T3 and T4. Diagnostically, T3 concentration is more sensitive to certain thyroid conditions than T4. While T4 levels are a sensitive (and superior) indicator of hypothyroidism, T3 blood levels better define hyperthyroidism. Because T3 concentration in serum changes faster and more markedly than T4, the T3 level is also an excellent indicator of the ability of the thyroid to respond to both stimulatory and suppressive tests. Under conditions of strong thyroid stimulation, the T3 level offers a good estimation of thyroidal reserve as well. This study evaluated the analytical performance of Atellica IM Total Triiodothyronine (T3) and Total Thyroxine (T4) assays on the Atellica CI Analyzer. The Atellica CI Analyzer is an automated, mid-throughput integrated chemistry and immunoassay analyzer employing Atellica CH and Atellica IM assays. Methods Atellica CI Analyzer uses the same reagents and calibrators as the Atellica IM Analyzer. Precision studies used native, mixed, and spiked human serum and quality control samples per CLSI EP05-A3. Repeatability and within-lab precision samples were tested in duplicate, 2 runs/day for 20 days (n=80) using one reagent lot and two analyzers. Reproducibility studies involved testing five replicates/run, 1 run/day for 5 days, and three lots on three analyzers (n=225/sample). Method comparison (MC) studies tested singlicate native human serum and contrived samples on Atellica IM and Atellica CI Analyzers per CLSI EP09c-ED3. Analytical sensitivity, limits of blank, detection, and quantitation (LoB, LoD, and LoQ(20%)) used three lots and one analyzer per CLSI EP17-A2. Linearity studies tested 9 levels of mixed high, and low samples (n=5/level) over 1 day/lot for two lots per CLSI EP06-ED2. Results T3 repeatability coefficients of variation (CV) were 1.8–7.3% and within lab 2.7–10.0% at 0.45–6.99 ng/mL (0.69–10.76 nmol/L). CVs for T4 repeatability were 1.5–4.2% and within lab 2.5–6.8% at 1.9–22.2 µg/dL (24.5–286.4 nmol/L). Reproducibility CVs for T3 were 2.4–8.9% at 0.45–6.96 ng/mL (0.69–10.72 nmol/L) and for T4 were 3.7–8.4% at 1.9–27.9 µg/dL (24.5–359.9 nmol/L). MC Weighted Deming regression equations were y=0.97x-0.02 ng/mL (y=0.97x-0.03 nmol/L ) at 0.44–7.50 ng/mL (0.68–11.55 nmol/L) (T3) (n=142; r=0.992) and y=1.04x-0.2 µg/dL ( y=1.04x-2.6 nmol/L) at 2.1–26.1 µg/dL (27.1–336.7 nmol/L ) (T4) (n=118; r=0.995). Analytical Sensitivity, LoB, LoD, and LoQ were 0.10, 0.20, 0.40, and 0.40 ng/mL (0.15, 0.31, 0.62, and 0.62 nmol/L) (T3); and 0.3, 0.3, 0.5, and 1.0 µg/dL (3.9, 3.9, 6.5, 12.9 nmol/L) (T4). Linear range was 0.10–8.00 ng/mL (0.15–12.32 nmol/L) (T3) and 0.3–30.0 µg/dL (3.9–387.0 nmol/L) (T4). Conclusion Evaluation of the Atellica IM T3 and T4 assays using the Atellica CI Analyzer demonstrated acceptable analytical performance and acceptable concordance compared to the Atellica IM Analyzer.