Determination of Vitamin D3Metabolites Using High-Performance Liquid Chromatography or Immunoaffinity Chromatography

Quantification of circulating 25-hydroxyvitamin D by liquid chromatography-tandem mass spectrometry

Hypovitaminosis D is a highly prevalent condition and quantification of serum 25-hydroxyvitamin D3 is accepted to be the most useful marker for the assessment of the individual vitamin D status. Due to the increasing awareness of the prevalence and potential health consequences of hypovitaminosis D, the request numbers for 25-hydroxyvitamin D quantification are growing rapidly in many countries. Automated protein binding assays (based on the use of vitamin D-binding protein or antibodies) for the quantification of 25-hydroxyvitamin D3 are available which enable convenient high-throughput analyses in a routine setting; there is, however, substantial concern about accuracy and analytical reliability of these assays. Several LC-MS/MS methods for the quantification of 25-hydroxyvitamin D3 in serum have been described and in a growing number of clinical laboratories this technology is used routinely for vitamin D monitoring. It is justified to assume that LC-MS/MS enables more reliable analyses of 25-hydroxyvitamin D concentrations compared to protein binding assays. In particular the ability to co-quantify the naturally occurring 25-hydroxyvitamin D3 and 25-hydroxyvitamin D2 which is derived primarily from food fortification is a relevant advantage of LC-MS/MS over protein binding assays. This review describes the background of 25-hydroxyvitamin D measurement, compares published LC-MS/MS methods, discusses problems, strengths and limitations of these assays and compares the application characteristics of LC-MS/MS with those of protein binding assays and HPLC-UV.

HPLC method for 25-hydroxyvitamin D measurement: comparison with contemporary assays

BACKGROUND

The concentration of 25-hydroxyvitamin D [25(OH)D] in serum has been designated the functional indicator of vitamin D (VitD) nutritional status. Unfortunately, variability among 25(OH)D assays limits clinician ability to monitor VitD status, supplementation, and toxicity.

METHODS

We developed an HPLC method that selectively measures 25-hydroxyvitamin D2 [25(OH)D2] and D3 [25(OH)D3] and compared this assay with a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, a competitive protein-binding assay (CPBA) on the Nichols Advantage platform, and an RIA from Diasorin.

RESULTS

For the new HPLC assay, between-run CVs were 2.6%-4.9% for 25(OH)D3 and 3.2%-13% for 25(OH)D2; recoveries were 95%-102%; and the assay was linear from 5 microg/L to at least 200 microg/L. Comparison data were as follows: for HPLC vs LC-MS/MS, y = 1.01x - 4.82 microg/L (Sy/x = 4.93 microg/L; r = 0.996) for 25(OH)D3, and y = 0.902x - 0.566 microg/L (Sy/x = 2.56 microg/L; r = 0.9965 for 25(OH)D2; for HPLC vs Diasorin RIA, y = 0.709x - 5.86 microg/L (Sy/x = 7.35 microg/L; r = 0.7509); and for HPLC vs Nichols Advantage CPBA, y = 1.00x - 3.60 microg/L (Sy/x = 32.7 microg/L; r = 0.6823).

CONCLUSIONS

The new HPLC method is reliable, robust, and has advantages compared with the Nichols Advantage CPBA and the Diasorin RIA. The Nichols Advantage CPBA overestimated or underestimated 25(OH)D concentrations predicated on the prevailing metabolite present in patients' sera.