Tissue transglutaminase - anything above zero?

I had my tissue transglutaminase test and hadn't eaten much gluten before (I had some bread a few times a week previously after many weeks of no gluten). My numbers came back as <1.9. The value is <19.90CU. So, is this test at all reliable as I didn't have much gluten before, or does anything above zero show some level of intolerance? I wondered if my number should have been absolute zero if I have no gluten sensitivity?

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Thanks so much for your help Annonymous, I appreciate it. I think that explains it so thanks. Have a good day yourself