Some people are negative for thyroid peroxidase antibodies but may be positive for thyroglobulin antibodies so negative thyroid peroxidase doesn't conclusively rule out autoimmune thyroiditis (Hashimoto's).
It could be helpful to have vitamin D, folate, B12 & ferritin tested. These are commonly low with thyroid, or may give similar symptoms in their own right.
If GP is reluctant to do these then Medichecks offer testing. Many of us get these tested along side full Thyroid in the Thyroid plus ultra vitamin test £99
When you did this test, did you do it as early in morning as possible & fasting?
As Clutter says - where is TG antibodies test result
Though as you say you have RA it might be positive due to that anyway. A high thyroglobulin antibodies test can be due to several autoimmune conditions, or have no apparent cause.
Content on HealthUnlocked does not replace the relationship between you and doctors or other healthcare professionals nor the advice you receive from them.
Never delay seeking advice or dialling emergency services because of something that you have read on HealthUnlocked.