Vitamin D and LC-MS/MS in the news
The New York Times recently reported on a major laboratory testing recall at Quest Diagnostics for falsely elevated 25-hydroxy vitamin D levels (1). Quest Diagnostics helped pioneer the use of liquid chromatography-tandem mass spectrometry for clinically measuring serum vitamin D. Therefore, the recall appropriately raises concerns regarding highly complex mass spectrometric methods. Importantly, many care providers have wondered whether other laboratories that perform a tandem mass spectrometric assay for vitamin D (like our reference laboratory at the University of Washington), could have issues similar to those experienced by Quest.
It should be pointed out that Quest Diagnostics has not provided exact details of their quality control failure and therefore any conclusions drawn from the recall are conjecture. However, the New York Times mentioned a problem with calibrators used by at least one of the Quest laboratories performing vitamin D testing. Currently, there are no available external proficiency testing programs for vitamin D in the United States, and, while NIST is developing a standard reference material, it has not yet been formulated and released. Therefore, laboratories must design their own calibrators and proficiency testing programs. Some laboratories rely on internal proficiency testing programs. Unfortunately, these programs fail to detect systematic bias that occurs when control materials and calibrators degrade over time. This could possibly explain the recent problems at Quest. At the University of Washington, we have helped develop a voluntary round-robin external proficiency testing program with other laboratories in the Pacific Northwest region that also perform vitamin D testing. In addition, we periodically perform comparisons with a reference laboratory outside the Pacific Northwest, Mayo Clinical Laboratories in Rochester, MN, to help ensure that our results do not drift over time.
Tandem mass spectrometry is without a doubt the most accurate method for quantifying vitamin D in patient samples. There are many laboratories who take the time and energy to validate their assay with other laboratories and provide reliable testing services for their patients. Hopefully, the events at Quest Diagnostics will help persuade laboratorians that external proficiency testing is beneficial to patients. Additionally, they may help motivate NIST to complete the formulation of their vitamin D preparation in a timely manner. If you have any questions regarding laboratory testing of 25-hydroxy vitamin D in patient specimens, please don’t hesitate to contact Dr. Andy Hoofnagle, MD PhD, Director of Clinical Mass Spectrometry at the University of Washington (ahoof@u.washington.edu).
1. Andrew Pollack “Quest Acknowledges Errors in Vitamin D Tests.” New York Times. January 7, 2009. (http://www.nytimes.com/2009/01/08/business/08labtest.html)