Hello and thanks for the query.
You are right in thinking that Thyroid autoantibodies should not be detectable in people who do not have thyroid autoimmunity,but that doesn't happen so every time

Your test indicates that you have thyroid autoimmunity. TPO Ab's are found in people with Graves' disease and with Hashimoto's thyroiditis, but are mostly associated with Hashi's, which causes hypothyroidism.

Your activity level is way below normal range. The lab's reference range indicates that a value over 9iu/ml would be considered positive, which usually translates to "indicating active disease XXXXXXX TPO Ab's are actually quite common in the population since something like 20% of all women have them even though those women may not have a clinically evident thyroid problem. When the level is high, it indicates an active disease state, and when levels are high, the patient almost always has abnormal labs (TSH, FT4, and FT3).

The family members of people with autoimmune thyroid disease frequently carry autoantibodies for either Graves' or Hashi's. If they never develop an active thyroid disease, they are said to have thyroid autoimmunity. Once they do develop an active disease (either hypo or hyper) then they are said to have an autoimmune thyroid disease. The reason is that carriers are predisposed to develop the disease, but something has to trigger it to cross over into an active, progressive disease course.

Years ago when these antibodies were discovered and lab tests were developed to detect them, the labs had to set "normal" reference ranges, and they usually tested the blood of many people and concluded that people became symptomatic at a certain Ab activity level. That level then became the "normal" cutoff for a disease diagnosis.
Your levels are absolutely normal and you should not worry.
It may be possible to have 0 IU/ ml in the blood.
I hope to have answered your query however you may revert to me for any other query.
Best of luck
Thanks

---