I don't understand IgA-tissue transglutaminase levels?

[mwragg45]

Hi,

I had a blood test which had positive results for "Omega Gliadin 17-mer IgG" & "Transglutaminase-6 IgG" which effects the brain so I follow a strict gluten free diet.

I have one question I am hoping somebody can help me with to try and understand and put to rest that it's not cealiacs too on top of gluten ataxia as I get all the gastro symptoms when consuming gluten. The question: I don't understand how they consider test results as negative for other antibodies (for example the ones to diagnose cealics disease) when the value is greater than 0. Is a detectable autoimune reaction not a reaction? I just don't understand how you can have "normal" levels of an autoimmune reaction?

My value for Transglutaminase-2 IgG is 0.46 (cyrex)

Thanks x

[Scott Adams]

Welcome to the forum. 

It would be helpful if you could include your full results, as well as the reference ranges for a positive test, as each lab handles these a bit differently.

In general, I agree with you that the cut off for a positive blood test is set by some sort of scientific consensus, but may not be very accurate. For example some people report TTG levels that are just below the cut-off marker for celiac disease, and their doctors tell them that they don't have to worry about gluten. This approach, in my opinion, is not accurate. Normal people do not generally have higher TTG levels at all, and elevated levels do indicate an autoimmune reaction that is abnormal. My daughter fell into this category, and ultimately went gluten-free without an official celiac disease diagnosis, as it was the only thing that offered her symptom relief. Her TTG levels were just below the cut off marker.

[RMJ]

When celiac blood tests were developed, the scientists would take blood samples from people with and without active celiac disease as determined by biopsy, and test those samples on their blood test.  They would look at the results, and choose a cutoff for positive vs negative that maximized the number of results that were correct, as based on biopsy results.

Also, this type of test typically doesn’t report a “0”.  Usually the lowest result is reported as less than some number (< #). That number is typically the limit of quantitation.  At low values the accuracy of such tests for giving a quantitative result decreases.  There will be a limit of detection and a limit of quantitation which is a bit higher.  At the limit of detection the test may show a result, but an accurate numerical value can’t be applied.  The limit of quantitation is the lowest value that is accurate enough to be reported as a number instead of <.

Hope this helps a little, although I realize it doesn’t answer your main question: How can having an amount of autoimmune antibody less than the cutoff be considered ok.