ABO titration Jenny White UK NEQAS (BTLP) Living donor kidney - - PowerPoint PPT Presentation

ABO titration Jenny White UK NEQAS (BTLP)

Living donor kidney transplant workshop 7/10/14

EQA Process

• Plan

exercise

• Prepare

samples

Exercise

• Test

exercise

• Report

results

Results

• Analyse

results

• Report

Report

• Review

results / learning points

Action

UK NEQAS Exploratory pilot - 2009

Recruited 52 participants from 15 countries

26 UK 26 non-UK

Belgium Cyprus Denmark Eire Finland Iceland Israel Netherlands Norway Portugal Oman Sweden Tunisia UK

20 ABOi renal transplant 13 BMT / HSCT 11 ABO HDN 5 Others

?Variability in practice ? Need for EQA

Titration method

Variables

• Technology (tubes, CAT etc.)
• End point
• Source of red cells used
• QC - titration of previous sample
• Testing method (IAT, DRT etc)

Variables within technology

• Red cell diluent
• Plasma / red cell ratio
• Red cell concentration
• Incubation time

2009 - huge variation between and within technology

Measuring IgG? IgM?

• Generalisations

IgM IgG

Cold (4oC) Warm (37oC) Direct agglutination at room temperature IAT

Anti-A and anti-B

• IAT result = IgG (+ IgM)

(used by 13/14 UK renal Tp centres)

• DRT result = IgM (+ IgG)
• IAT (DTT treated plasma) = IgG

2009 example UK NEQAS results

Quantifying antibody concentration Aubuchon et al

370C - Gel - AHG

Application of Aubuchon et al

°

UK NEQAS ABOT Pilot 2010 – to date

• Aim = to support ABOi transplant
• ABOi pilot EQA Scheme guided by ABOi SAG
• Development of standard technique

– IT and DRT DiaMed, prescribed volumes, end point etc.

– facilitate EQA – transferrable results across centres

• Developing ABO ‘standards’ with NIBSC
• Highlight variability in titres to clinicians

ABOi pilot 2012-13

4 exercises per year

• 3 plasma samples for titration vs. A cells provided
• Replicate samples in 3 consecutive exercises
• Duplicate sample within an exercise
• Reporting individual result to each lab and method medians
• Comparing in-house and standard techniques
• Questions on clinical use of results
• 69 labs (37 UK), 38 supporting ABOi transplant and 31 others

Example individual results

Inter laboratory results spanned a wide range, e.g.: 512 – 32000 by IAT for a high titre sample ABOT4 P1 (standard median 2048) 8 – 128 by IAT for low titre sample ABOT3 P3 (standard median 16)

Replicate samples over 3 exercises

% results for replicate samples the same or within 1 or more dilution

• 92% sets of standard IAT results within 1 DD cf. 66% IH IAT.
• 51% sets of standard DRT results within 1 DD cf. 68% DRT IH
• Only 1/3 sets of IAT DTT treated plasma was within 1 DD

Duplicate samples in the same exercise

95.5% results by DRT and 98.8% by IAT were within one dilution 78% of IAT (non-DTT) results and 72% DRT results identical

In-house median vs. std median (IAT)

The IAT BioVue median result was higher than that for the IAT ‘standard technique’ (DiaMed) in 11/12 (92%) samples

• Median for each sample by each IH technology assigned a score of 1 for

each dilution above or -1 for each dilution below the standard median.

• Where median between two dilutions, results either side assigned 0.5.
• Scores totalled to give a cumulative score.

Clinical use of results

• 14 UK transplant centres surveyed in 2013
• Maximum patient ABO antibody titres
• 128-4096 for acceptance ABOi renal transplant programmes
• 2-16 for a transplant to go ahead on the day

Example of IAT results (for a single EQA sample) submitted by laboratories providing ABO titration results to these centres

• No correlation

result with cut-off values

2012/13 ABOT Pilot – outcomes (1)

• Still variation in in-house methodology
• Increasing use of standard technique - EQA and clinical
• Measurement of IgG / IgM? – DRT, IAT, IAT DTT treated
• Errors in A subtyping (one exercise)

– 2 labs supporting ABOi programs mistyped A2 cells as A1

2012/13 ABOT Pilot – outcomes (2)

• IAT more reproducible than DRT
• Standard IAT results more reproducible than IH IAT results
• Std. results tighter range (closer to method median) than Tube
• BioVue IAT titre consistently higher than std. IAT titre

2012/13 ABOT Pilot – outcomes (3)

Variation in practice (14 UK centres - ABOi renal Tp)

• Max titre for admission to ABOi program (128 – 4096)
• Max titre for suitability on day of Tp (2-16)
• ‘Cut-offs’ values do not correlate with EQA titres

Conclusions

• Need EQA
• Need reference preparations for anti-A and anti-B
• Need standardisation to make results transferrable

between centres and to allow equitable access to ABOi transplant programmes1

• Need to find a safe way to implement standardisation

1 No progress in ABO titer measurement: time to aim for a reference? A.

Bentall et al, Letter to the editor, Transplantation, volume 97, number 3, February 15 2014