Quality assessment of vitamin D metabolite assays used by clinical and research laboratories.
The Vitamin D External Quality Assessment Scheme (DEQAS) was launched in 1989 and monitors the performance of 25-hydroxyvitamin D (25-OHD) and 1,25- dihydroxyvitamin D (1,25(OH)2D) assays. In April 2015 a pilot scheme for 24,25-dihydroxyvitamin D (24,25(OH)2D) was introduced. The 25-OHD scheme is accuracy - based with target values assigned by the NIST Reference Measurement Procedure (RMP) for 25-OHD2and 25-OHD3. A similar method is used to assign values for 3-epi-25-OHD. Five samples of human serum are distributed quarterly to over 1000 participants in 58 countries (April 2016) and clinical laboratories are expected to submit results within approximately 5 weeks. Research laboratories with assays run less frequently are not given a deadline. Archived samples with NIST- assigned values are also available. Performance is assessed on the first four samples with the fifth reserved for investigations e.g. recovery experiments or to assess the influence of other serum constituents such as lipids. DEQAS provides rapid feedback, with an on-line preliminary report available immediately after a participant submits results and a comprehensive report soon after the results deadline. In 2015, DEQAS investigations revealed that several 25-OHD immunoassays under-recovered 25-OHD2and 25-OHD results were falsely low on a sample with a modestly raised triglyceride concentration. An RMP for 1,25 (OH)2D is not yet available and results are judged against the Method Mean. Free advice is available from the DEQAS Advisory Panel which includes experts on methodology and biostatistics. DEQAS collaborates closely with the Vitamin D Standardization Program (VDSP) and both organizations have successfully worked with participants and manufacturers to improve the accuracy of vitamin D assays.
Imperial College Healthcare NHS Trust, Clinical Biochemistry Department, Charing Cross Hospital, London W6 8RF, UK. Electronic address: b.carter1@which.net.
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Carter
DEQAS Advisory Panel, Charing Cross Hospital, London W6 8RF, UK.
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Berry
DEQAS Advisory Panel, Charing Cross Hospital, London W6 8RF, UK.
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Durazo-Arvizu
DEQAS Advisory Panel, Charing Cross Hospital, London W6 8RF, UK.
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Gunter
DEQAS Advisory Panel, Charing Cross Hospital, London W6 8RF, UK.
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Jones
Imperial College Healthcare NHS Trust, Clinical Biochemistry Department, Charing Cross Hospital, London W6 8RF, UK.
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Jones
DEQAS Advisory Panel, Charing Cross Hospital, London W6 8RF, UK.
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Makin
Imperial College Healthcare NHS Trust, Clinical Biochemistry Department, Charing Cross Hospital, London W6 8RF, UK.
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Pattni
DEQAS Advisory Panel, Charing Cross Hospital, London W6 8RF, UK.
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Phinney
DEQAS Advisory Panel, Charing Cross Hospital, London W6 8RF, UK.
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Sempos
Imperial College Healthcare NHS Trust, Clinical Biochemistry Department, Charing Cross Hospital, London W6 8RF, UK.
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Williams
D002623:Chemistry Techniques, Analytical / Q000379:methods*; D019411:Clinical Laboratory Techniques / Q000379:methods; D004872:Ergocalciferols / Q000097:blood*; D006801:Humans; D011786:Quality Control; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014815:Vitamins / Q000097:blood*
D004872:Ergocalciferols; D014815:Vitamins; D014807:Vitamin D; C097949:1,25-dihydroxyvitamin D; C028140:24,25-dihydroxyvitamin D2; C104450:25-hydroxyvitamin D
1,25-Dihydroxyvitamin D; 24,25-Dihydroxyvitamin D; 25-Hydroxyvitamin D; Accuracy- based; DEQAS; Triglyceride