We use the same policy as Steve. All new positive IgA-tTG antibody results are confirmed by endomysial slide IIF (irrespective of the numerical result). This also equates to about a slide per week in our laboratory.
Our weak range is 11-20 U/mL but this is entirely arbitrary and we do not use this for clinical decision making as we have not confirmed the range empirically.
We use the Orgentec IgA-tTG ELISA: It does not seem to suffer from 'false positives' as much as some of the other assays and an IgA-tTG +ve, IgA-endomysial -ve antibody result is a rare event in our lab. I'm aware this is more of an issue in other centres, this may be assay or population specific. We do not have a particularly large paediatric population.
The literature does state that the IgA-endomysial IIF is marginally more specific but also marginally less sensitive than the IgA-tTG but I suspect this is very assay/manufacturer dependent. I would not consider the endomysial IIF the gold standard test for coeliac; the duodenal biopsy is considered the 'gold standard'.
Kind regards
Adrian
Dr Adrian Heaps BSc MSc PhD DIC FRCPath
Consultant Clinical Scientist & Clinical Lead (Immunology)
Department of Virology & Immunology
Cumberland Infirmary
Newtown Road
Carlisle
Cumbria
CA2 7HY
Cumberland Infirmary contact:
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Tel: 01228 814367 / 814645
Fax: 01228 814864
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The NCUHT Pathology Handbook can be found here
James Cook University Hospital contact:
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-----Original Message-----
From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Steve Holding
Sent: 17 June 2018 18:50
To: [log in to unmask]
Subject: Re: Coeliac serology
We check all positive TTG with EMA.
About 2% of our requests are positive so this amounts to a slide a week.
This would be no different if we just confirmed 'weakly positive' results.
Difficult to define 'weakly positive' but I use <30 u/mL (double the lower limit of the ref. interval, which is <15 u/mL).
We use Biorad Bioplex 2200 TTG-IgA/G assays.
Best Wishes
Steve
Steve Holding PhD FRCPath
Consultant Clinical Scientist (Clinical Immunology)
Honorary Professor, Hull York Medical School
Blood Sciences, Pathology Dept, Hull and East Yorkshire Hospitals, Anlaby Road, Hull, HU3 2JZ
o +44 (0)1482 607710
-----Original Message-----
From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of CLIFFORD-MOBLEY, Oliver (UNIVERSITY HOSPITALS BRISTOL NHS FOUNDATION TRUST)
Sent: 15 June 2018 17:21
To: [log in to unmask]
Subject: Coeliac serology
Dear mailbase,
NICE NG20 recommends confirming weakly positive IgA TTG antibodies with IgA endomysial antibodies (EMA).
How have other centres defined and verified the TTG weakly positive range? We recently switched TTG assay and during our verification found that some TTG results above the manufacturer's stated weakly positive range were negative by EMA. Therefore we are currently confirming all positive TTG by EMA and not defining a 'weakly positive' range - are any other centres doing the same thing?
The alternative we could consider is to define the upper limit of the TTG weakly positive range such that it has 100% concordance with EMA positivity. However the question that arises from this is whether EMA should be considered the gold standard: I understand that it has a greater specificity than TTG for CD but I also believe that a false negative EMA is still possible.
Many thanks,
Oliver Clifford-Mobley FRCPath
Principal Clinical Scientist
Department of Clinical Biochemistry
University Hospitals Bristol NHS Foundation Trust
T: 0117 342 7833
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