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Vitamin D testing continues to have lots of varition between systems – Nov 2012

Evaluation of two automated immunoassays for 25-OH vitamin D: Comparison against LC-MS/MS.

J Steroid Biochem Mol Biol. 2012 Nov 29.
Hsu SA, Soldo J, Gupta M.
Cleveland Clinic, Department of Clinical Pathology, Cleveland, OH 44195, United States.

BACKGROUND/METHODS: A total of 95 human serum specimens, and a 12 specimen precision panel, were measured by 2 automated immunoassays (investigation use only DiaSorin LIAISON(®) 25 OH Vitamin D TOTAL Assay [LSN], and Siemens ADVIA Centaur(®) Vitamin D Total (VitD) assay [Centaur]) and the results compared against LC-MS/MS [LCMS] used as the reference method (Esoterix Inc.). For functional sensitivity and precision, 12 serum specimens [range 1.2-148ng/mL] were run in six replicates [N=30] or four replicates [N=20], respectively, for 5 consecutive days.

RESULTS: Passing-Bablok fit and Difference plot analysis [N=92] showed that although both immunoassays had comparable correlation coefficient [r] values to LCMS (0.936 and 0.933), the LSN assay results were statistically equivalent to those given by LCMS (slope 0.93, intercept -2.5), whereas the results of the Centaur assay showed overall significant assay bias compared to LCMS (slope 1.30, intercept -15.8) and this bias was more significant for doses <30ng/mL by LCMS [bias -30.4%; 95% limits of agreement -72.4% to 11.7%]. For specificity, based on 25-OHD(2) and 25-OHD(3) levels assessed by LCMS, we divided the specimens into 2 groups, one with detectable 25-OHD(2) [Group 1, N=41] and the other with no detectible 25OHD(2) [Group 2, N=51]. The 2 groups showed comparable correlation coefficient [r] values between the methods, but showed significant differences in slope: Centaur [1.48 with group 1 and 1.18 with group 2] compared to LSN [0.91 with Group 1 and 0.96 with Group 2]. LSN demonstrated better precision [total CV range 5.5-10.0%] compared to Centaur [total CV range 11.0-16.3%]. Functional sensitivity was calculated per EP-17A: 2.15ng/mL by LSN and 4.57ng/mL by Centaur.

CONCLUSIONS: Though there was good overall correlation, substantial bias was present in Centaur. Although LSN had a slope and intercept that was not significantly different than LCMS, Centaur had a significantly higher slope in specimens containing measurable 25-OHD(2) levels, a large negative intercept and a significant negative dose bias for doses <30ng/mL by LCMS, suggesting the Centaur assay would report a higher frequency of patients with apparent vitamin D insufficiency/deficiency at the low end and apparent vitamin D toxicity at the high end compared against LCMS. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Copyright © 2012 Elsevier Ltd. All rights reserved.

PMID: 23202147

Note: 100 nmol = 40 ng

Level of quantification generally 10 nmol, but one is much higher, 50 nmol

Day-to-day variation is an acceptable 7nmol for blood level of about 170 nmol

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Frequently failed to correctly say blood level was > 40 nmol (false negative)

10X fewer times failed to correctly say blood level was < 40 nmol (false positive)

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Ideally all colored bars in a group should be the same height

These are worst-case examples of discrepancies between readings

Sample 4: most measured about 70 nmol (28 ng), but one measured 19 nmol ( 8 ng)

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Attached files

ID Name Comment Uploaded Size Downloads
2221 Finn F2.jpg admin 18 Mar, 2013 65.13 Kb 1318
2220 Finn T4.jpg admin 18 Mar, 2013 33.96 Kb 1323
2219 Finn T1.jpg admin 18 Mar, 2013 66.52 Kb 1389
2218 Compare vitamin D test - Finland.pdf admin 18 Mar, 2013 327.58 Kb 7336