The research findings – presented at The Endocrine Society's 94th Annual Meeting – revealed that two newly approved blood tests for vitamin D were inaccurate in at least 40% of laboratory specimens analysed.
Dr Earle Holmes of Loyola University Stritch School of Medicine, USA, and his colleagues examined how well the new tests – Abbott Architect and Siemans Centaur2 – performed on 163 randomly selected blood samples. The team reported that in 40% of the Abbott Architect specimens and 48% of the Siemans Centaur2 specimens, results were inaccurate by over the maximum allowable error of plus-or-minus 25%.
Such inaccuracies could lead to misdiagnoses of patients, said Holmes.
"These inaccuracies also could confound efforts to identify the optimal levels of vitamin D for good health," he added.
Testing vitamin D
Holmes noted that doctors and nutritional advisors are increasingly ordering blood tests to measure vitamin D - often referred to as the sunshine vitamin - revealing that such tests are now among the most frequently ordered medical tests.
Such an increase in testing may result from recent scientific reports that a growing percentage of the global population has low vitamin D status, in combination with fresh research to link insufficient vitamin D with higher risks of certain diseases such as diabetes, heart disease, multiple sclerosis, osteoporosis and certain cancers.
The researchers said the new tests tended to overestimate vitamin D deficiency.
According to gold-standard LCMS measurements, 33 of the 163 specimens showed vitamin D deficiency. However the Abbott test showed that 45 specimens had vitamin D deficiency while the Siemens test showed that 71 subjects had vitamin D deficiency.
Such inaccuracies could lead to over diagnosis of vitamin D deficiency, Holmes said.
"There has been an exponential increase in the number of vitamin D tests ordered for patients," said the US-based researcher. "But our study of two newly approved tests showed they had pretty poor performance."