Standardizing 25-hydroxyvitamin D data from the HunMen cohort

Standardization of 25-hydroxyvitamin D (25OHD) values is still a challenge. We propose standardization by correction of the measured 25OHD values using the linear regression bias from the National Institute of Standards and Technology (NIST) 'total' target values reported by Vitamin D External Quality Assessment Scheme (DEQAS). Our approach could perhaps be a practical solution to the anomaly surrounding non-standardized 25OHD values. Standardization of 25OHD values is still a challenge. We propose standardization by correction of the measured 25OHD values using the linear regression equation derived from the analysis of relationship between total 25OHD values measured by the methodology used by the laboratory and the NIST total target values (TV) reported by the DEQAS for all 5 of the DEQAS samples in a given survey. We applied our approach to standardize total 25OHD values of the HunMen cohort. All 206 samples for the HunMen cohort were evaluated using the automated Liaison DiaSorin total 25OHD chemiluminescence immunoassay (CLIA). The timing of these measurements coincided with that of the October 2015 DEQAS survey using samples 481 to 485. Following standardization, the mean total 25OHD changed from 53 to 62 nmol/L and the prevalence of hypovitaminosis D (< 75 nmol/L) decreased significantly from 84 to 72%. A simple approach readily applicable at the routine diagnostic laboratory could perhaps be a practical solution to the anomaly surrounding non-standardized 25OHD values.