Newer Vitamin D Tests Often Inaccurate: Study
Faster, Less Expensive Tests May Overestimate Vitamin D Deficiency
Study Details continued...
Holmes says vitamin D2 seems to confuse the tests.
He says the tests' inability to accurately measure that form of the vitamin means that doctors can't tell if their patients are getting any benefit from it or if they're taking their supplements as directed.
"You can't tell if you're making a difference for the patients," Holmes says.
In absolute numbers, the reference test showed 33 patients out of 163 were deficient in vitamin D, while the Abbott test showed 45 people were vitamin D deficient, and the Siemens test pointed to deficiency in 71 patients.
Current guidelines by the Institute of Medicine state a vitamin D level of at least 20 nanograms per milliliter (ng/ml) in the blood as adequate for bone health and overall health. However, other experts, including Holmes, feel that a normal level is 30 ng/ml or higher.
In a statement issued in response to the study, Abbott, the company that makes the Architect test, says the results of the current study depend on the use of a reference test that is "a very hands-on, labor intensive, manual procedure for which there currently is no standard protocol or calibration method. As a result, this leads to variability of results from lab to lab."
"In current studies ... as well as in recent proficiency surveys, the ARCHITECT Vitamin D test showed excellent precision and reproducibility of results from lab to lab," the statement reads.
Siemens is checking the study's accuracy: "Siemens Healthcare Diagnostics is committed to delivering high-quality solutions and services to our customers that enable health care professionals to accurately diagnose, treat, and monitor patients. We are closely reviewing the validity of the claims made in this report along with the design of the methods and analysis used to develop them."
The wholesale price of the newer tests is estimated to cost around $20 to $25, although patients and insurance companies may be charged more. That's about half the cost of the older reference test, experts said, which wholesaled for about $50 a test.
This study was presented at a medical conference. The findings should be considered preliminary, as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.