Performance evaluation of two immunoassays for 25-hydroxyvitamin D

Although immunoassays in measuring 25-hydroxyvitamin D [25(OH)D] have been improved recently, relatively large differences are still seen between results of 25(OH)D measured by immunoassays and by liquid chromatography-tandem mass spectrometry (LC-MS/MS). In the present studies, we compared two immunoassays with LC-MS/MS for measuring 25(OH)D concentrations. Concentrations of 25-hydroxyvitamin D(2) [25(OH)D(2)] and 25-hydroxyvitamin D(3) [25(OH)D(3)] in serum samples from 59 healthy subjects were measured by two immunoassays including Siemens ADVIA Centaur Vitamin D Total (Centaur) and Roche Elecsys Vitamin D Total (Elecsys) and LC-MS/MS. To determine the cross reactivity of Elecsys and Centaur toward 25(OH)D(2), a dosage of 200,000 IU vitamin D(2) was given after first sampling. Serum samples were obtained 30 days later and concentrations of 25(OH)D(2) and 25(OH)D(3) were measured again. The results showed poor agreement between the immunoassays and LC-MS/MS in 25(OH)D(2) and 25(OH)D(3) measurements. The percentage of 25(OH)D(2) cross-reactivity was 45.3% for Centaur and 41.2% for Elecsys and there was no significant difference between Centaur and Elecsys. In conclusion, Centaur and Elecsys perform unsatisfactorily in measuring 25(OH)D levels, especially for 25(OH)D(2) cross-reactivity. Therefore, clinicians need to be aware of the underestimation of vitamin D status when using these immunoassays for measuring individuals supplemented with vitamin D(2).