= Emerging. More than 5 years before clinical availability. (26.62%)
= Expected to be clinically available in 1 to 4 years. (38.91%)
= Clinically available now. (34.47%)
MSACL 2020 US : Jin

MSACL 2020 US Abstract

Topic: Tox / TDM / Endocrine

Poster Presentation
Poster #33a
Attended on Wednesday at 15:00

An Investigation of Positive Bias in Our Mass Spectrometry-based 1α,25-dihydroxyvitamin D Assay

Zhicheng Jin (Presenter)
Houston Methodist Hospital

>> POSTER (PDF)

Presenter Bio(s): Zhicheng Jin received his PhD in analytical chemistry from Purdue University in 2010. He completed two postdoctoral trainings, one at Johns Hopkins University and one at Case Western Reserve University. He then worked at Cleveland HeartLab, now part of Quest Diagnostics, as a research scientist. Dr. Jin is currently a clinical chemistry fellow in the Department of Pathology and Genomic Medicine at Houston Methodist Hospital.

Authors: Zhicheng Jin, PhD, Ashley N. Siverly, and Xin Yi, PhD
Department of Pathology and Genomic Medicine, Houston Methodist Hospital, Houston, TX 77030

Abstract

Introduction

A 1α,25-dihydroxyvitamin D (DHVD) test is used to assess the level of the biologically active form of vitamin D in patients with chronic renal disease or for differential diagnosis of hypercalcemia. The DHVD assay is challenging because there are numerous isomers present in patient specimens, and the active form has very low circulating concentrations (picomolar). Our hospital is currently using a Cookson-type triazolinedione derivatization protocol followed by LC-MS/MS quantification to determine 1α,25-dihydroxyvitamin D2 and 1α,25-dihydroxyvitamin D3 levels in serum specimens (1). While investigating a positive comparison bias for DHVD assay results, we discovered that the reference laboratories had adopted a new methodology. We thus modified our methodology to address these discrepancies.

Methods

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is considered the “gold standard” for quantification of vitamin D metabolites in complex matrices. Our original method started with solid-phase extraction and derivatization using 4-phenyl-1,2,4-triazoline-3,5-dione. The derivatized complex mixtures were chromatographically separated on Acuity BEH C18 columns (1.7 µm, 2.1x100 mm) using a Shimadzu UHPLC system coupled to a Sciex Qtrap 5500 instrument operating in triple quadrupole mode. Recent studies showed that immunoaffinity purification may reduce an interference metabolite that was co-eluting with DHVD peaks. However, we optimized liquid chromatographic separation to resolve interference peaks that may lead to positive bias of the DHVD results.

Results

Our recent in-house alternative proficiency tests showed a positive bias in comparison to DHVD send-out test. Specifically, the results of our calibrators were acceptable, while the majority of patient specimens showed positive bias. We performed a thorough investigation, ruled out assay issues, and finally determined that the change was likely not within our lab. Two months later, the reference laboratories reported a modified sample preparation method that incorporated immunoaffinity isolation steps. Their decreased DHVD levels in patient specimens were consistent with the protocol change. These results indicated that our method was likely overestimating DHVD if there was an interference that may be co-eluting with the targeted analyte. Recent studies showed that 4β,25-dihydroxyvitamin D and 1α,25-dihydroxy-3-epi-vitamin D have the same mass-to-charge ratio as 1α,25-dihydroxyvitamin D and may cause bias in the quantification of DHVD. Based on the retention time, we suspected that an interference peak was possible due to the presence of 4β,25-dihydroxyvitamin D (2). By using a phenyl-hexyl LC column and slightly extending the LC gradient, we were able to separate an interference peak from the DHVD peak. The assay results using our updated LC-MS/MS method were consistent with results from the reference laboratory.

Conclusion

We identified the root cause of positive bias in our DHVD assay. Optimizing chromatographic separation allowed us to address the deviation in a timely manner. Our quantification assay will be revalidated after the method modification.

References

1. Laha TJ, etc. Characterizing and harnessing antibody cross-reactivity for the immunoaffinity purification of analytes prior to multiplexed liquid chromatography-tandem mass spectrometry. Clin Chem. 2012, 58(2):1711-1716.

2. Wang Z, etc. Simultaneous measurement of plasma vitamin D3 metabolites including 4β,25-dihydroxyvitamin D3 using liquid chromatography-tandem mass spectrometry. Anal Biochem. 2011, 418(1):126-133.


Financial Disclosure

DescriptionY/NSource
Grantsno
SalaryyesHouston Methodist Hospital
Board Memberno
Stockno
Expensesno
IP Royaltyno

Planning to mention or discuss specific products or technology of the company(ies) listed above:

no