20 percent change in vitamin D levels of critically ill during a 24 hour period
Do random estimations of vitamin D3 and parathyroid hormone reflect the 24-h profile in the critically ill?
Intensive Care Medicine
Volume 38, Number 1, 177-179, DOI: 10.1007/s00134-011-2415-x
Correspondence
Bala Venkatesh, Ben Davidson, Katherine Robinson, Ranald Pascoe, Charles Appleton and Mark Jones
These were people expected to be in the ICU for more than 24 hours.
Author feels that a single vitamin D test is not appropriate.
Note: 50 nmol = 20 ng; 100 nmol = 40 ng



See also VitaminDWiki
Vitamin D test results vary as much as 30 ng between test labs – Jan 2012
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
Day to Day blood test variation less than 8 percent - Aug 2010