From a slide presented by From Center for Disease Control
Isotope Dilution Tandem Mass Spectrometry Coupled to Liquid Chromatography (LC-MS/MS)
Precision <8% day-to-day variation
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See also VitaminDWiki

• All items in Vitamin D Test 46 items as of Jan 2012
• Vitamin D test results vary as much as 30 ng between test labs – Jan 2012
• Vitamin D tests had poor agreement – yet again – April 2011
• Panel Discussion on Vitamin D and Tests - 2011
• Vitamin D measurements of individuals vary by 3 ng within 6 days – June 2011
• Vitamin D blood testing within plus or minus 7 percent – Mar 2010 variation between labs
• Comparison of vitamin D blood tests – worse case off by 15% – Aug 2010 variation between labs
• 20 % change in vitamin D levels of critically ill during a 24 hour period – Oct 2011 has the following graph