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Thread: Working out MU for a Blood Group???

  1. #1
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    Working out MU for a Blood Group???

    From discussions with colleagues across UK it appears that very much time and effort is being placed into working out the MU for a blood group result. My questions are:
    1. What is the purpose of identifying MU for a blood group?
    2. A blood group is a qualitative test not quantitative, so wouldn't MU be irrelevent?
    3. If an MU is required, how do you calculate/ factor in sampling errors from the clinical areas to address wrong blood in tube errors?
    4. If an MU is needed- will this be stated in the User Manual? If not, why not?
    5. How would an MU be written on a report or in the User Manual- eg Patient is group A+ ( or there is a X % chance they may not be ???!)
    6. What is the clinical significance of working out the MU for this test? Is this actually going to give anyone ( clinicians/ staff/ patients) confidence in the process?

    I'm often wrong about things, but really want to understand WHY this is required ? Again, are we ALL misinterpreting the clauses/ NCs etc and creating more unnecessary work within the labs , many of who are already under staffing capacity and can't get important basic improvement tasks done?

    Some clarification would be helpful.

    Many thanks
    Rashmi

  2. #2
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    Also , majority of patients are tested twice!!on separate samples
    dont start me on this one!

  3. #3
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    Thanks EClarke- I know how you feel!

    To continue this saga, and thanks to colleagues for forwarding me their spreadsheets on calculations, though I still havenít been told WHY itís being done.

    I understand that analysers create data/ numbers from the visual images of each individual reagent; this data is either interpreted into a recognized blood group or not depending on the reaction strength rules (0,1+to 4+) applied.

    Some questions:
    1. If MU is needed, whenever the analyser camera is re-calibrated / changed/ software updated/ or annually, will you re-calculate?
    2. How do Westgard rules apply to blood grouping? (For antibody screening, we can apply this rule based on the weak antibody controls run. We use 3+ reaction required +/-1 strength, anything outside follows out of spec testing protocols).
    3. How do you apply MU for a manual group- or is this exempt? This testing probably has a higher error rate than automation.

    I will not be working MU for this test, as far as I can make sense, my test is controlled by our ABO/D reagent controls, and analyser settings ensure that only certain reaction strengths are interpreted and these are checked, ( eg for our D typing potentiated reagents the analysers are set to interpret 0= RhD-Neg and 4+ as RhD Pos , anything less is rejected, so we donít miss the weak-Ds for reflex testing).

    My point isÖÖ There is so much time being needlessly wasted across 300+ labs and no guidance given, or if given, is inconsistent.

    Some thoughts/hints:
    1. The best assessors/ inspectors always guide staff on approaches to address NCs, keeping it as simple as possible. Try to teach, not confuse please!
    2. Some formal and consistent guidance is needed across UK- how about posting on this Forum?
    3. Standard terminology would also be helpful.

    Many thanks
    Last edited by Rashmi; 8th Aug 2019 at 11:38 PM.

  4. #4
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    Please see reply from UKTLC colleagues regarding this issue, and I will post some further info on ways to achieve a simple approach.
    Thank you all
    Rashmi

    MU Blood Grouping test


    Query raised with UKAS – Formal response from UKAS requested around MU for the Blood Grouping test.

    Response:

    Unfortunately UKAS are not Consultants and cannot provide a formal definitive response on this matter. However the approach that many labs have taken and that assessors have accepted can be shared as guidance.
    This test is not qualitative. Although results are + or -, they are graded 1-4 and they are dependent on antibody concentration and antigenicity.
    This can lead to using simple Stats, there is no need for complicated ones. The scoring does come from the strength of the reactions, but it is the effect on the clinical decision level that needs to be looked at. Hundreds of 4+ results does not really mean anything. However, weak reactions at 1+ may sometimes be interpreted as 0, it is at this level of detection that uncertainty lies, i.e. are you certain of the result?
    Guidelines say that labs need to be able to detect 0.1 IU/ml anti-D, which often comes to a 2+ or 3+ strength in practice. But would you issue anything with a 1+ reaction? Using the NIBSC anti-D for titration can give the results to look at for certainty.
    Data from IQC can be used to calculate imprecision uncertainty. Statistical appropriate numbers should be used.

    Tables and grids can be created to record reaction data from all the platforms and stats performed. You may get one analyser which is persistently giving out lower gradings- this may be due to temperature or spin speed, as we know that these are not calibrated by manufacturers.
    QC grading data should also be trended. Many labs are just recording + and -, not the gradings, and therefore not trending.

    ISO guidance is available – ISO/TS 20914:2019 – Medical Laboratories – Practical guidance for the estimation of measurement uncertainty. This document provides practical guidance for the estimation and expression of the measurement uncertainty (MU) of quantitative measurand values produced by medical laboratories. This document also applies to the estimation of MU for results produced by qualitative methods which include a measurement step.

  5. #5
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    Further responses from UKTLC Colleagues:

    Regarding how UoM might be determined for a test that produces truly qualitative results, it was discussed that antigen and antibody concentrations could possibly be used to apply UoM when close to the limits of detection.
    The general feeling is that if internal controls are used, setting a limit at which the reaction strength is acceptable +/- one reaction grade is a good approach, and anything outside of this warrants investigation. We also think that when UKAS refer to UoM for transfusion tests, they in fact mean 'confidence', since there are so many stages in a transfusion test that lead to the end result.

    Please also see link to a presentation from UKAS- has some useful info on working out Kleihauer MU.

    https://www.ukneqash.org/download/543/UKNEQASHaematologyAnnualMeeting2019MsCarolStearn-MeasurementUncertainty


    Last edited by Rashmi; 24th Nov 2019 at 04:43 PM.

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