Quest Discusses Use of Mass Spec Methodology

Moving Vitamin D testing to mass spectrometry provides analytically precise results of D2 and D3

CEO SUMMARY: Having made the decision to perform nearly all Vitamin 25(OH) D testing by liquid chromatography–tandem mass spectrometry (LC–MS/MS), Quest Diagnostics Incorporated found the transition to be challenging. That was particularly true as the volume of Vitamin D specimens tripled at the nation’s largest lab company during the period May 2006 to May 2008. Medical Direct Richard Reitz, M.D., shares insights about Quest’s experience with LC–MS/MS.

HAVING DECIDED, ABOUT TWO YEARS AGO, to migrate Vitamin 25(OH) D testing onto an internally-developed assay, Quest Diagnostics Incorporated was willing to discuss its experience in working with this methodology.

In a recent interview, Richard E. Reitz, M.D., Medical Director, Nichols Institute, Quest Diagnostics’ esoteric testing center, and Medical Director, Endocrinology/ Metabolism, Toxicology at Quest’s laboratory in San Juan Capistrano, California, shared information about why Quest Diagnostics decided to use liquid chromatography–tandem mass spectrometry (LC-MS/MS, or mass spectrometry) as its preferred methodology for Vitamin 25- hydroxy D testing.

“Our interest in mass spectrometry has been ongoing,” said Reitz. “Since the 1990s, mass spectrometry has played a growing role in steroid hormone testing at Nichols Institute, for example. LC– MS/MS has been a high performance methodology for us.

“This experience encouraged us to look at how LC–MS/MS could be used in Vitamin 25(OH) D testing,” he continued. “The technology has the capability of providing very precise analytical results. One benefit of this in Vitamin D testing is the ability of LC–MS/MS to identify and measure both D2 and D3 components of the total Vitamin 25(OH) D.”

Quest Diagnostics saw this capability of mass spectrometry as one benefit when compared to the radioimmunoassay (RIA) and the immunoassay (IA) methods. “By comparison, the IA and RIA methods of testing for Vitamin 25(OH) D are not able to recognize the D2 and D3 components separately,” stated Reitz.

Use For Vitamin D Testing

Following this evaluation, Quest Diagnostics made the decision to make its internally-developed LC–MS/MS assay for Vitamin 25(OH) D testing the primary method. Approximately two years ago, it introduced this assay to physicians and the clinical community.

The timing of introducing the mass spectrometry method coincided with a huge increase nationally in demand for Vitamin D testing. The volume of Vitamin D test requests arriving at Quest Diagnostics and other laboratories has increased rapidly in recent years. For example, in news interviews, Quest Diagnostics has stated that the volume of Vitamin D tests referred to it tripled in the 24 months between May 2006 and May 2008.

Home Brew Assay

“It is important to note that mass spectrometry is not standardized for Vitamin D testing” observed Reitz. “For example, Mayo Clinic uses mass spectrometry for Vitamin D testing and has its own calibrators, just as we at Quest Diagnostics have our calibrators.

“The internal quality control program here at Quest constantly scrutinizes and evaluates the test runs at all sites and across all instrument systems,” stated Reitz. “As the LC–MS/MS assay for Vitamin 25(OH) D was brought up at selected laboratories in our system, we maintained a tight QA/QC process.

“Quest Diagnostics has recognized that, starting in early 2007 and into 2008, for some periods of time for a small percentage of tests, there were potentially inaccurate results at certain of our testing sites,” acknowledged Reitz. “A thorough review of Vitamin D results reported throughout this time was conducted.”

Recognized The Need To Act

According to Reitz, a broad definition was used. “We defined ‘inaccurate’ to be any result which had the potential to be wrong,” he said. “This was the starting point for identifying patients that would be notified of the possibility of an inaccurate result and then offered a retest of their Vitamin D at no charge.”

Quest Diagnostics, in assessing the issues that produced what it defined as inaccurate results, determined that its quality management process needed to be strengthened across the laboratory sites within its system where mass spectrometry Vitamin D testing is performed.

“Accuracy and reproducibility over time are very important for every laboratory,” stated Reitz. “We saw the opportunity to improve our internal proficiency testing (PT) at all sites. We have intensified our internal program of using blinded daily samples to provide a timely quantitative check on the quality of our Vitamin D testing. We verify our calibrators and keep our quality control within tight parameters.”

Another element in Vitamin D testing is the ongoing publication of clinical stud- ies that link Vitamin D to an increasing number of diseases and health conditions. As a result of these new studies, some Vitamin D researchers are calling for guidelines to change. These researchers recommend that some individuals may need significantly higher levels of Vitamin D.

Optimal Reference Range

“We are confident that our results are accurate,” stated Reitz. “As we nail down these accurate standards, the separate question is ‘what is the optimal reference range for Vitamin D?’ For example, is the floor 30 ng/mL, or is it higher? We can’t make that statement because it is something upon which the medical community must agree.”

On behalf of Quest Diagnostics, Reitz was candid in acknowledging that the laboratory company had delivered results it deemed to be inaccurate for a period of time. “The message here is that, in addressing this issue, Quest Diagnostics is taking the high road with patients and physicians” stated Reitz. “Offering to retest patients who may have received inaccurate results is the right thing to do.

“Further, I want to stress that, as Quest Diagnostics has tightened its quality management, it can verify precision, accuracy, and the clinical relevance of the answers it delivers to physicians and patients every day,” he concluded.

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