Multicenter Comparison of Seven 25OH Vitamin D Automated Immunoassays

A Novel Approach for Routinely Assessing Laboratory Sigma Metrics for a Broad Range of Automated Assays

BACKGROUND

Sigma metrics have been adapted for the clinical laboratory to incorporate observed accuracy, precision, and total error allowed. The higher the Sigma level for a process, the better performance that process has. A limitation of studies assessing Sigma metrics is that they are performed on a small number of well-controlled systems.

METHODS

An algorithm was developed to extract QC data and derive the Sigma metric for 115 analytes from sites connected to the QuidelOrtho E-Connectivity® database. The median of these results was then used to derive the Sigma metric for each assay.

RESULTS

In this analysis, 79 out of 115 (68.7%) of the assays assessed achieved 6 Sigma or better and 98 out of 115 (85.2%) achieved 5 Sigma or better.

CONCLUSIONS

This study has demonstrated a methodology that can be used to condense Sigma metrics from hundreds of analyzers into a single metric of assay quality. Because these analyzers are running in working laboratories from around the world, this analysis can serve as a baseline for understanding the assay performance achieved in the presence of variabilities such as lab-to-lab, instrument-to-instrument, material handling, environmental conditions, and reagent lot. The significant number of assays demonstrating high Sigma levels did so despite this variation. The ability of the methods reported here to include hundreds of analyzers represents a novel approach for assessing Sigma metrics in clinical laboratories.

Serum 25-hydroxyvitamin D measurement: Comparative evaluation of three automated immunoassays

Objectives: the different analytical methods for measurement of serum 25-hydroxyvitamin D (25(OH)D) are not yet fully harmonized and no consensus exists on a threshold of 25(OH)D defining a deficiency status. In this study, we compared the results from the assays of serum 25(OH)D performed with three different methods to evaluate the presence of potential biases and how much these biases can influence the assignment of patients to specific 25(OH)D deficiency/sufficiency categories. Design and Methods: Liaison 25(OH) Vitamin D Total (DiaSorin Liaison XL), Elecsys Vitamin D Total II (Roche Elecsys) and Lumipulse G25(OH) Vitamin D (Fujirebio Lumipulse G1200) were used. Methods comparability was established performing Passing-Bablok regression and Bland-Altman analysis to prove whether the differences found were lower than the preliminarily pre-established maximum acceptable bias. Results: all Passing-Bablok regressions exhibited the presence of a proportional and constant systematic error. Bland-Altman analysis revealed biases well above the maximum acceptable bias, so the 25(OH)D concentrations measured were not comparable. To evaluate whether the three methods had the same ability to classify patients into different categories of vitamin D levels, we categorized results obtained by each method in reference classes. Lumipulse categorized most patients into the class with the lowest 25(OH)D concentrations (<20 ng/mL) whereas Elecsys ranked the lowest number. Conclusions: Liaison XL and Elecsys have shown good accuracy compared to Lumipulse in measuring 25(OH)D levels. Nevertheless, the assays were not interchangeable due to the lack of comparability of results as well as to the disagreement in classification of hormone deficiency or sufficiency.

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Three immunometric assays for the measuring of serum 25(OH)Vitamin D were compared.

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Two of three assay show good accuracy whereas the third only fair.

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Due to the lack of comparability of the results, the assays were not exchangeable.

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Assays are at odds in the classification of hormone deficiency or sufficiency.

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Efforts will be required in the future to improve the immunoassays harmonization.

Clinical Significance of Analysis of Vitamin D Status in Various Diseases

Vitamin D plays a role not only in the proper functioning of the skeletal system and the calcium-phosphate equilibrium, but also in the immune system, the cardiovascular system and the growth and division of cells. Although numerous studies have reported on the analysis of vitamin D status in various groups of patients, the clinical significance of measurements of vitamin D forms and metabolites remains ambiguous. This article reviews the reports analyzing the status of vitamin D in various chronic states. Particular attention is given to factors affecting measurement of vitamin D forms and metabolites. Relevant papers published during recent years were identified by an extensive PubMed search using appropriate keywords. Measurement of vitamin D status proved to be a useful tool in diagnosis and progression of metabolic syndrome, neurological disorders and cancer. High performance liquid chromatography coupled with tandem mass spectrometry has become the preferred method for analyzing the various forms and metabolites of vitamin D in biological fluids. Factors influencing vitamin D concentration, including socio-demographic and biochemical factors as well as the genetic polymorphism of the vitamin D receptor, along with vitamin D transporters and enzymes participating in vitamin D metabolism should be considered as potential confounders of the interpretation of plasma total 25(OH)D concentrations.

Looking beyond linear regression and Bland-Altman plots: a comparison of the clinical performance of 25-hydroxyvitamin D tests

Background:

The systematic evaluation of the clinical concordance of various 25-hydroxyvitamin D (25OHD) testing methods is presented. The need for this approach is raised by the discrepancies in the analytical performance of the available assays.

Methods:

The analytical and clinical performance of six automated 25OHD assays and an in-house liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was investigated. Leftover serum samples (n=162, SA: n=114) were analyzed and all 21 assay combinations were evaluated. The utility of Cohen’s κ values was assessed by transforming them into minimum percentage agreement (MPA). McNemar’s hypothesis test was employed for testing the symmetry of the disagreeing classification outcomes within each method pair.

Results:

Depending on the assay method, the ratio of results classified as positive (<20 ng/mL) was 13.5%–40.0%. The percentage agreement (PA) was 74.1%–92.6%. Compared to other methods, significantly more hypovitaminosis cases were delivered by DiaSorin Liaison® 25 OH vitamin D Total (DL) and significantly fewer by IDS-iSYS 25-Hydroxy Vitamin DS (II). The strongest clinical concordance was exerted by II vs. LC-MS/MS. The κ-derived MPA showed close similarity to the PA scores. McNemar’s tests confirmed the asymmetry of the disagreement in the classification in 14 method combinations.

Conclusions:

The presented approach allows the prediction of the clinical consequences of a 25OHD method transfer. Differences in the clinical classification of assay results are likely encountered when transferring to a new method, even between assays standardized according to the Vitamin D Standardization Program (VDSP) Reference Method Procedure (RMP).

Blood Sampling Seasonality as an Important Preanalytical Factor for Assessment of Vitamin D Status

BACKGROUND

The measurement of vitamin D is now commonplace for preventing osteoporosis and restoring an appropriate concentration that would be effective to counteract the occurrence of other human disorders. The aim of this study was to establish whether blood sampling seasonality may influence total vitamin D concentration in a general population of Italian unselected outpatients.

METHODS

We performed a retrospective search in the laboratory information system of the University Hospital of Parma (Italy, temperate climate), to identify the values of total serum vitamin D (25-hydroxyvitamin D) measured in outpatients aged 18 years and older, who were referred for routine health check-up during the entire year 2014.

RESULTS

The study population consisted in 11,150 outpatients (median age 62 years; 8592 women and 2558 men). The concentration of vitamin D was consistently lower in samples collected in Winter than in the other three seasons. The frequency of subjects with vitamin D deficiency was approximately double in samples drawn in Winter and Spring than in Summer and Autumn. In the multivariate analysis, the concentration of total vitamin D was found to be independently associated with sex and season of blood testing, but not with the age of the patients.

CONCLUSIONS

According to these findings, blood sampling seasonality should be regarded as an important preanalytical factor in vitamin D assessment. It is also reasonable to suggest that the amount of total vitamin D synthesized during the summer should be high enough to maintain the levels > 50 nmol/L throughout the remaining part of the year.