Aims

The overall aim of DEQAS is to ensure the analytical reliability of 25 hydroxyvitamin D (25OHD) and 1,25 dihydroxyvitamin D (1,25(OH)2D) assays. This is achieved through:

  • The distribution of serum pools at regular intervals
  • Statistical analysis of submitted results
  • Appropriate manipulation of pools to provide information on assay specificity and recovery
  • Assignment of GC-MS 'target values' to selected pools (25OHD)
  • Helping participants and manufacturers in the evaluation of methods through the provision of samples, technical support and impartial advice
  • Offering advice and support to participants experiencing difficulties in achieving an acceptable level of assay performance.
  • Providing a forum for the exchange of information on all aspects of vitamin D methodology

    Organisation

    Serum is harvested from blood donated by patients undergoing therapeutic venesection for haemochromatosis or polycythaemia. Permission to use the blood has been obtained from the local Ethics Committee and the UK Department of Health. All patients have given their informed consent.

    Liquid serum pools (5) are distributed quarterly (January, April, July, October) at ambient temperature. All pools are screened for hepatitis B, C and HIV before despatch.

    Laboratories are given approximately 5 weeks to return results. Data are statistically trimmed to produce an All-Laboratory Trimmed Mean (ALTM), SD and CV. The final report is sent by e-mail or post and is also available to participants on the Internet (see below). The report includes the trimmed mean, SD and CV for the major method groups, together with individual histograms.

    An on-line reporting system was introduced in 2004. A dedicated server hosted by a commercial company ensures security and frequent backup of the DEQAS database. Participants submitting results via the Internet have immediate access to updated statistics and histograms without having to wait for the final report.

    DEQAS results are confidential and will not be disclosed to a third party without permission of the participant.

    The Occasional Analyst

    Colleagues (eg. vitamin D researchers) whose workload would not justify full participation in DEQAS, but who wish to check the accuracy of their assays, can purchase samples as and when required. A full statistical analysis is provided. Please e-mail the DEQAS administrator for further details (administrator@deqas.org).

    Advisory Panel

    The Advisory Panel for the DEQAS was set up in 1997 and consists of scientists with acknowledged expertise in vitamin D methodology and/or external quality assessment schemes.

    The panel will advise the DEQAS organiser on:

  • All aspects of sample preparation and distribution
  • The investigation of specific aspects of vitamin D methodology
  • Statistical analysis and presentation of data
  • Setting of performance targets.

    Members of the Panel are available to offer advice to participants with queries arising from their DEQAS performance or other matters related to vitamin D.

    Initial contact should be made through the DEQAS Organiser.

    • Proficiency Certificate

    A proficiency certificate is issued annually to those laboratories meeting the performance target set by the DEQAS Advisory Panel for 25OHD assays.