25-Hydroxyvitamin D Assays: The Quest For Accuracy
Clinical Chemistry 55: 1300-1302, 2009. First published May 7, 2009; 10.1373/clinchem.2009.125906
Graham D. Carter1,a
1 DEQAS Organizer, Imperial College Healthcare NHS Trust, London, UK.
Address correspondence to the author at: Imperial College Healthcare NHS Trust, Oncology/Endocrine Laboratory, Charing Cross Hospital, Fulham Palace Rd., London W6 8RF, UK. Fax 44-(0)20-8846-7007; e-mail b.carter1 at which.net.
The first 20% of the full text of this article appears below.
The recently reported difficulties experienced by Quest Laboratories (1) have once again highlighted concerns about the reliability of 25-hydroxyvitamin D (25-OH-D)1 results, particularly those generated by liquid chromatography–tandem mass spectrometry (LC-MS/MS), the method used by Quest. In the New York Times article of January 8, 2009 (1), a spokesman for Quest admitted that some erroneous results were reported because of problems with calibration and that some of their laboratories "did not always follow proper procedures." One suspects these shortcomings were influenced by the eye-watering number of 25-OH-D requests received by Quest: 500 000 per month according to John Cannell, quoted in a pathologist’s newsletter (2).
This unfortunate episode dramatically emphasizes the need for a rigorous internal quality-assurance system. Such a system must include a role for a quality manager (preferably independent) who should be responsible for the monitoring of internal quality controls and the results of external proficiency-testing schemes. Some of us learned of the Quest problem through John Cannell’s Vitamin D Council newsletter sent out in July 2008 (3).
In the same issue, he was promoting, without apparent irony, a commercial kit designed to "accurately" measure 25-OH-D in patient-generated blood spots, a technique that cannot easily be monitored by external proficiency-testing schemes.
Those of us who work in clinical laboratories know that "stuff happens." At some stage in our careers, many of us will probably have to contact clinical colleagues to admit reporting errors of some sort, although almost certainly not on the scale reported in the New York Times. It is to Quest’s credit that they admitted the problem and offered to repeat these analyses free of charge.