A-042 Comparison of the Second-Generation Parathyroid Hormone Assays: ELSA-PTH and Alinity i Intact PTH

Abstract

Abstract Background Measurement of parathyroid hormone (PTH) level is essential in diagnosing and treating hyper- and hypoparathyroidism. Because of the various presenting forms of PTH (biologically active full-length PTH and also PTH fragments) in the blood and the lack of standardization, there can be a difference in results between the assays even when the same assay generation is used. We compared the two second-generation PTH assays, ELSA-PTH and Alinity i Intact PTH, and evaluated the analytical performance of Alinity i Intact PTH, newly adopted in the laboratory. Methods For method comparison, 56 remnant samples of routinely ordered sera for the PTH test were collected. ESLA-PTH assay tested on Gamma-10 contains the anti-[39-84, amino acids] PTH antibody coated on the tube, which captures PTH in the sample and is measured by the radioactivity through the bound I125-labelled anti-[1-34] PTH antibody. Alinity i Intact PTH assay performed on Alinity i system uses the anti-[39-84] PTH antibody coated on a paramagnetic microparticle and is analyzed by the emitted light through the captured acridinium-labeled anti-[1-34] PTH antibody. The correlation between the two tests was evaluated. Additionally, precision, linearity, and reference range verification were analyzed to investigate the performance of the Alinity i Intact PTH assay. Results Of the 56 samples, 35 (62.5%) were requested by the Nephrology department for evaluating chronic kidney disease, 16 (28.6%) by the General surgery department during and after parathyroid and thyroid surgery, and 5 (8.9%) by other departments. 52.3% of the patients were female, and the median age was 61.5 years (interquartile range: 45.3–71). The median values of ELSA-PTH and Alinity i Intact PTH were 69.0 pg/mL and 101.9 pg/mL, respectively, and the PTH values of Alinity i Intact PTH were significantly higher (P < 0.0001) by the Wilcoxon test. The Pearson correlation coefficient (r) was 0.959, and the average difference between the two tests was 78.57 pg/mL. In Alinity i Intact PTH, the coefficient of variation obtained at each low (10.5 pg/mL), medium (66.6 pg/mL), high (254.6 pg/mL) levels were 1.9%, 2.4%, and 1.8% for repeatability, and 2.03%, 2.71%, and 2.65% for within-laboratory precision, respectively. Linearity was observed within the analytical measuring range of 3–3000 pg/mL. The reference range (15–68.3 pg/mL) recommended by the manufacturer was validated with 20 normal sera. Conclusion The PTH values of Alinity i Intact PTH were significantly higher than those of the ELSA-PTH, and both assays showed a strong correlation. Additionally, the Alinity i Intact PTH assay demonstrated acceptable analytical performance.