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Clinical Reclassification of Vitamin D Status Across Three Automated Immunoassays After Comparability Study
Adina Huțanu1,2, Ana-Maria Fotache Țurcan3, Oana Roxana Oprea1,4
1Department of Laboratory Medicine, George Emil Palade University of Medicine, Pharmacy, Science, and Technology of Targu Mures, 540142 Târgu Mureș, Romania.
Nutrients
|July 28, 2026
Summary
Routine vitamin D tests show significant variability between lab platforms, impacting patient diagnosis. Measurement uncertainty leads to reclassification, especially near the 20 ng/mL threshold for insufficiency.
Area of Science:
- Clinical Chemistry
- Laboratory Medicine
- Immunoassay Technology
Background:
- Variability in routine 25-hydroxyvitamin D (25(OH) vitamin D) immunoassays can affect clinical interpretation.
- Clinical decision thresholds for vitamin D status are particularly sensitive to assay differences.
Purpose of the Study:
- To evaluate analytical comparability and clinical interchangeability of three automated immunoassay platforms for total 25(OH) vitamin D.
- To assess the impact of assay differences on patient reclassification around clinical decision thresholds.
Main Methods:
- Analysis of 83 serum samples across three automated immunoassay platforms (CLIA and ECLIA).
- Assessment of between-method comparability and clinical agreement.
- Evaluation of patient reclassification rates at thresholds of 20 ng/mL (insufficiency) and 12 ng/mL (severe deficiency).
Main Results:
- Significant systematic differences were observed between the immunoassay methods.
- A high rate of patient reclassification occurred between electrochemiluminescent assay (ECLIA) and chemiluminescent assay (CLIA) methods.
- Expanded measurement uncertainty created a clinically relevant gray zone around decision thresholds.
Conclusions:
- Routine immunoassays for total 25(OH) vitamin D are not fully interchangeable in clinical laboratories.
- Measurement uncertainty contributes to clinically significant patient reclassification, particularly around the 20 ng/mL insufficiency threshold.
