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Correlation among 25-hydroxy-vitamin D assays.

N Binkley¹, D Krueger, D Gemar

¹Osteoporosis Clinical Center and Research Program, University of Wisconsin, 2870 University Avenue, Madison, WI 53705, USA. nbinkley@wisc.edu

The Journal of Clinical Endocrinology and Metabolism

|March 6, 2008

Summary

Clinical laboratories show similar 25-hydroxy-vitamin D [25(OH)D] measurements. Using a single calibrator improves but does not eliminate lab variability, suggesting a target of >30 ng/ml for vitamin D status.

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Published on: December 9, 2015

Area of Science:

Clinical Chemistry
Laboratory Medicine
Endocrinology

Background:

Circulating 25-hydroxy-vitamin D [25(OH)D] is the standard clinical measure of vitamin D status.
Significant between-laboratory variability in 25(OH)D assays can complicate patient care and interpretation of results.

Purpose of the Study:

To assess the agreement of 25(OH)D measurements across different clinical laboratories.
To evaluate if simple calibration can enhance the consistency of 25(OH)D measurements between laboratories.

Main Methods:

Serum samples from healthy volunteers and a single calibrator were analyzed for 25(OH)D in four laboratories using HPLC, LC-MS/MS, and RIA.
Linear regression and Bland-Altman analyses were employed to compare results, with the laboratory exhibiting the lowest interassay CV designated as the reference.

Main Results:

High correlation (R²=0.81-0.99) was observed between laboratories, but modest between-laboratory bias (2.9-5.2 ng/ml) was noted.
Most laboratories reported higher 25(OH)D values compared to the reference laboratory.
Employing a single calibrator and correction factor effectively reduced mean bias for two laboratories.

Conclusions:

Clinical laboratory measurements of 25(OH)D are generally similar, despite some variability.
While a single calibrator can improve consistency, it does not fully resolve between-laboratory differences.
Clinicians are advised to target 25(OH)D levels above 30 ng/ml, considering both assay variability and individual patient status.