Background: We compared total 25-OH vitamin D status measured by DiaSorin Liaison and tandem mass spectrometry (LC-MS/MS) among patients with high and low 25-OH vitamin D(2).
Methods: Total 25-OH vitamin D was measured in plasma containing high (>25 nmol/l or >50%, n=26) and low (<2.5 nmol/l, n=29) 25-OH vitamin D(2) using DiaSorin Liaison and an LC-MS/MS method using NIST 972-verified calibrators. Samples were classified as vitamin D adequate (total 25-OH vitamin D ≥50 nmol/l), and inadequate or deficient (<50 nmol/l) by each method. Deming and multiple linear regression were used to compare methods.
Results: Samples were significantly more likely to be classified as inadequate or deficient by DiaSorin Liaison (36%) vs LC-MS/MS (9%). This increased in the presence of high 25-OH vitamin D2 (42% vs 0%). Total 25-OH vitamin D by DiaSorin Liaison was 26.0 nmol/l lower than LC-MS/MS, which increased to 34.1 nmol/l among samples with high 25-OH vitamin D(2). This was attributed to lower recovery of 25-OH vitamin D(2) (proportional bias=0.64 nmol/l) by DiaSorin Liaison, independent of D(3) (proportional bias=0.86 nmol/l).
Conclusions: Patients were more likely to be classified as vitamin D inadequate or deficient by DiaSorin Liaison compared to an LC-MS/MS method, which was in part due to the presence of 25-OH vitamin D(2).
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