Some vitamin D tests may give misleading results despite progress made in recent years to improve the quality of these assays, according to the US Centers for Disease Control and Prevention .
For example, some assays measure other compounds besides 25-hydroxyvitamin D, which can falsely elevate results of some blood samples, Sugahara reported. Thus, some tests may be misclassified, with results seen as sufficient from samples that should have indicated a vitamin D deficiency. "They have literally thousands of diseases they have to be able to recognize and diagnose," Sempos said."They should be able to count on the laboratory system to give them accurate and precise data.". It helps by"nudging manufacturers in the right direction," he said.
US scientists use two main types of technologies to measure vitamin D in the blood, Sugahara said. One is mass spectrometry, which separately measures 25-hydroxyvitamin D2 and D3 and sums the values. The other type, immunoassay, measures both compounds at the same time and reports one result for total 25-hydroxyvitamin D.
These are improved results compared with 2019 data, in which mass spectrometry–based assays had a mean bias of 1.9% and immunoassays had a mean bias of 2.4%, the CDC toldVitamin D tests are widely administered despite questions about their benefit for people who do not appear likely to be deficient of it.
They noted that the influential US Preventive Services Task Force also has raised doubts about widespread use of vitamin D tests.