Re-certification of hydroxyvitamin D standards by isotope pattern deconvolution.

BACKGROUND: Vitamin D testing in analytical clinical laboratories has been experiencing a rapid increase of demand over the last years, as it plays a key role in several disorders. Due to the narrow ranges of medical significance regarding its concentration levels in human serum, accurate and precise determinations of vitamin D metabolites are required.

METHODS: We present an isotope dilution mass spectrometry quantification method for the re-certification of routine commercial standards used in method validation steps, isotope pattern deconvolution (IPD) based on LC-MS/MS.

RESULTS: IPD allowed to compensate for the observed biases of +4.7% for 25(OH)D3, -29% for 25(OH)D2 and -30% for 24,25(OH)2 D3 standard concentrations, respectively in an easy, cheap and straightforward way.

CONCLUSIONS: Is has been observed that, in some cases, discrepancies may exist between stated purity or amount of routinely used commercial standards and actual values, which would lead to unwanted bias in the developed methodologies. The present correction has helped meeting the regulations established by international standardization programs, including Vitamin D Standardization Program (VDSP).