Published in:
01-01-2022 | Hypophosphatemic Rickets | Original Article
Performance evaluation of the new chemiluminescent intact FGF23 assay relative to the existing assay system
Published in: Journal of Bone and Mineral Metabolism | Issue 1/2022
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Introduction
This study assessed the performance of a new fully automated immunoassay for fibroblast growth factor (FGF) 23 (Determinar CL FGF23 CL) among healthy individuals and those with chronic hypophosphatemia compared with the previous assay (Kainos FGF23 KI).
Materials and methods
A total of 380 serum samples from healthy participants were collected to determine the reference range of FGF23 levels with CL. A total of 200 serum samples from 22 hypophosphatemic patients were collected simultaneously to compare the difference in FGF23 levels between CL and KI. The Mann–Whitney U test and linear regression analysis were adopted to assess the differences and linearity between the two assays.
Results
The median FGF23 levels among healthy individuals was 31.7 (interquartile: 26.4–37.5) pg/mL. When the reference range was calculated as the mean ± 2 standard deviation (2SD), it was 16.1–49.3 pg/mL. A total of 363 individuals (96%) among normal cases fell in this range. Among 200 samples from patients with chronic hypophosphatemic disorder, the median FGF23 levels analyzed by CL and KI were 123.0 (90.2–237.7) and 172.5 (115.8–290.7) pg/mL. KI yielded significantly higher FGF23 values than CL (p < 0.001). A linear regression model revealed the correlation between KI (x) and CL (y), which had a slope of 0.76 with a y-intercept of −0.32 and high linearity (R2 = 0.99).
Conclusion
The new measurement kit yielded lower FGF23 values when compared with the previous assay. Clinicians should consider this discrepancy when they assay intact FGF23 values with CL.