Interlaboratory comparison with a reference measurement procedure (RMP) for determining 24,25-dihydroxyvitamin D₃ in...

Area of Science:

• Clinical Chemistry
• Mass Spectrometry
• Vitamin D Metabolism

Background:

• Accurate measurement of 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) is crucial for understanding vitamin D status.
• Standardization of 24,25(OH)2D3 assays is needed due to variability in laboratory results.

Purpose of the Study:

• To evaluate the performance of liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods for 24,25(OH)2D3 determination across multiple laboratories.
• To compare laboratory results against a National Institute of Standards and Technology (NIST) reference measurement procedure (RMP).

Main Methods:

• An interlaboratory comparison study involving five laboratories using LC-MS/MS methods.
• Analysis of human serum samples and Standard Reference Materials (SRMs).
• Statistical evaluation using Ordinary Deming linear regression and Bland-Altman analysis against NIST RMP values.

Main Results:

• Three of five laboratories demonstrated good agreement with the NIST RMP, with regression slopes between 0.972-1.003 and low mean bias.
• Two laboratories showed significant positive bias (slopes 1.158-1.214).
• The Centers for Disease Control and Prevention (CDC) method showed strong agreement with the NIST RMP (slope=0.984, R²=0.996, mean bias=-0.092 nmol/L).

Conclusions:

• The CDC LC-MS/MS method for 24,25(OH)2D3 measurement is reliable and agrees well with the NIST RMP.
• The CDC method's performance suggests its potential for improving the accuracy of reference values in the Vitamin D External Quality Assessment Scheme (DEQAS).
• Further standardization efforts are warranted to ensure consistent and accurate 24,25(OH)2D3 measurements across clinical laboratories.