Accurate measurement of serum folate is essential for the diagnosis and management of various disorders. This study aims to investigate the between-method differences of four immunoassays and a rapid isotope-dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) method.
Roche Cobas (USA), Abbott Alinity i2000 (USA), Beckman Coulter Access (USA), Mindray CL-6000i (China), and the ID-LC-MS/MS method were compared using 46 human serum samples. The results were analysed by Passing–Bablok regressions and Bland–Altman plots. A bias of 13.31% based on biological variation was used as the bias criterion.
All the within-run and total coefficients of variation (CVs) met the specification. The folate concentrations determined by all the assays were significantly different (p=0.0028). All assays had correlation coefficients over 0.97 with each other. The 95% confidence intervals (CIs) for the slope seldom contained 1 and few 95% CIs for the intercept contained 0 in the regression equations. Compared to ID-LC-MS/MS, the biases of all assays ranged from −20.91 to 13.56 nmol/L, and the mean relative biases ranged from −9.85 to 40.33%. The predicted mean relative biases at the medical decision levels rarely met the criterion.
Assays for serum folate had good correlations with each other but lacked good agreement. The accuracy and consistency of assays for serum folate should be measured and assessed routinely. Standardization work to improve the accuracy of serum folate assays, such as the extension of traceability to reference methods or materials, calibration standardization efforts, and assay-adjusted cut-offs should be promoted.
Funding source: The National Key Research and Development Program of China
Award Identifier / Grant number: 2018YFC1002204
We are grateful for the kind help and technique guidance of engineers from Abbott, Roche, Beckman, and Mindray.
Research funding: The National Key Research and Development Program of China (2018YFC1002204).
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Competing interests: Authors state no conflict of interest.
Informed consent: This study was approved for the exemption from informed consent.
Ethical approval: The study was approved by the Ethics Committee of Beijing Hospital and the Ethics Committee of Nanjing Maternal and Child Health Hospital.
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The online version of this article offers supplementary material (https://doi.org/10.1515/cclm-2021-1283).
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