[MON-372] Analytical Performance Characteristics of Two New Automated Immunoassays for 25 Hydroxy Vitamin D

Earle W Holmes, Jean Garbincius, Kathleen M McKenna. Loyola University Stritch School of Medicine, Maywood, IL; Loyola University Medical Center, Maywood, IL.

A marked increase in the demand for 25 hydroxy vitamin D (25OHD) testing has led to the development of several new immunoassays for the measurement of 25OHD in un-extracted serum. We have compared 25OHD results measured by the Abbott Architect (ARC) and the Siemens Centaur2 (CT2) immunoassays with total 25OHD results determined by liquid chromatography/tandem mass spectrometry(LCMS) (Quest Diagnostics, Wood Dale, IL 60191). The study sample consisted of 163 randomly selected clinical specimens (123 f, median age: 54yr and 40 m, median age: 59 y) submitted for 25OHD testing between 3/2 and 3/7/11. 98 of the specimens contained only 25OHD3 and 65 contained both 25OHD3 and 25OHD2.
The results of linear regression analysis of the total 25 OHD results measured by each immunoassay (y) as compared to the total 25OHD (25OHD2+25OHD3) by LCMS (x) were as follows: ARC: r2=0.41; SE= 7.8ng/mL; slope=0.47+/-0.44; intercept= 11.4+/- 1.54 ng/mL.CT2: r2=0.76; SE= 8.7ng/mL; slope=1.12+/- 0.05; intercept= -8.3+/- 1.73 ng/mL. 33, 45, and 71 of the subjects in the study population had 25OHD results that indicated Vitamin D deficiency (<20 ng/mL) when measured by LCMS, ARC, and CT2, respectively. The magnitudes of the absolute biases between the total 25 OHD results determined by LCMS and results determined by either of the immunoassays for the 25OHD2-containing specimens showed an under-recovery of 25OHD2 by the ARC and an over-recovery of 25OHD2 by the CT2. The differences between the total 25OHD results measured by LCMS and ARC or CT2 exceeded the maximum recommended total allowable error (+/- 25%) for 25OHD measurements in 40%, or 48%, respectively, of the clinical samples that were tested.
Our results showed that both of these new FDA-approved immunoassays were characterized by high degrees of random variability and significant constant biases relative to an established LCMS method, inaccurate measurement of 25OHD2, and a failure to meet even a minimum quality standard for analytical bias for many of the clinical specimens we tested. The inaccuracy of these immunoassays at 25OHD levels in the lower part of the analytical measuring range would have led to a marked overestimation of the prevalence of vitamin D deficiency in our study sample. The widespread use of new analytical methods with poor analytical quality may confound efforts to establish reference values for 25OHD in health and efforts to evaluate the role of vitamin D insufficiency as a risk factor in disease.

Nothing to Disclose: EWH, JG, KMM

Date: Monday, June 25, 2012
Session Info: POSTER SESSION: Vitamin D: Assays, Clinical Trials & Physiologic Functions (1:30 PM-3:30 PM)
Presentation Time: 1:30 pm
Room: Expo

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