Although there have been general improvements since its inception in 2013, the Vitamin D Standardization Certification Program (VDSCP) continues to note inconsistencies in vitamin D test accuracy, leading to continued patient misclassification beyond 2022. Knowledge of these inaccuracies is essential for healthcare providers to further improve vitamin D testing and avoid misclassification.1
“Vitamin D testing can help health care professionals make correct diagnoses and appropriate treatment decisions for their patients. However, many clinical organizations and experts have raised concerns about the accuracy and reliability of vitamin D testing,” said Sugahara Otoe, CDC’s VDSCP manager, in a press release.2
The primary function of the VDSCP is to collect analytical data annually to review and evaluate the accuracy of vitamin D tests.
“Since 2013, the assays enrolled in the program have been improved overall and become better calibrated,” Sugawara continued.2
Key Takeaways
- The Vitamin D Standardization and Certification Program (VDSCP) continues to highlight inconsistencies in vitamin D testing accuracy.
- The researchers aimed to address CDC’s improvements in vitamin D testing over the years, while also identifying potential misclassifications.
However, as vitamin D testing continues to be overhauled over the years, misclassification continues as researchers fail to follow the Endocrine Society guidelines, which state that vitamin D levels below 50 nmol/L are considered deficient, while levels between 50 nmol/L and 75 nmol/L are considered insufficient.1
The researchers used these guidelines on samples testing for vitamin D levels of 55.1 nmol/L, which would be classified as insufficient, but 44% of results reported deficiency. Because of the misclassification and inaccurate results, the researchers used positive or negative calibration bias to evaluate the accuracy of the vitamin D assay.
Although there have been general improvements since its inception in 2013, the Vitamin D Standardization and Certification Program (VDSCP) continues to note inconsistencies in the accuracy of vitamin D tests. | Image credit: ratmaner / stock.adobe.com
“Since its inception, the program has seen improvements in calibration bias. In 2022, across all assays registered in the VDSCP, the average bias for mass spectrometry-based assays was 0.55% and the average bias for immunoassays was 0.86%. This indicates that assays registered in the VDSCP are overall well calibrated. However, improvements in calibration have made sample-specific inaccurate results more pronounced,” wrote the authors of the abstract presented at ENDO 2024, the Endocrine Society’s annual meeting.1
Read more: Vitamin D and COVID-19: an evidence-based review
In fact, some findings from the most recent review of the VDSCP indicate that while calibration has improved, it is still sporadic and not always 100% accurate, so it is important for researchers working on the VDSCP to get as close as possible to this accuracy threshold.
Moreover, these discrepancies in vitamin D testing have existed since the inception of the VDSCP, with previous studies analyzing the accuracy of liquid chromatography-tandem mass spectrometry reporting misclassification and inaccuracies approximately 10 years ago.
“Reliability (precision) and accuracy are of particular concern in epidemiological studies, where poor precision can lead to non-discriminatory misclassification bias and null results. Moreover, studies of the risks of vitamin D deficiency to human health often combine results from many different studies, where accuracy can be particularly problematic,” the study authors wrote.3
These findings highlight the need to improve the accuracy of the VDSCP. With testing biases improved, CDC can more easily identify sample-specific inaccuracies. It is these specific inaccuracies that the researchers address in their summary.
From improvements over the years to new inconsistencies recently uncovered in the VDSCP, CDC’s goal is to maximize overall testing accuracy while avoiding misclassification as much as possible.
“Although most vitamin D tests are effective, it is important for health care providers to be aware of potential discrepancies associated with vitamin D testing to avoid patient misclassification,” the summary authors conclude.1
Read more: Vitamin D deficiency may increase risk of gastrointestinal bleeding in patients taking blood thinners
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