I Have Hashimoto's. When I Was Diagnosed My Lab Results

I have Hashimoto's. When I was diagnosed my lab results for the thyroid antibodies were given in IU/ml. I recently had them retested and a different lab reported them in U/ml. I can not find the answer to whether these units are comparable and, if not, how to convert one to another so I can compare them. Can anyone help?
Didn't know I would have to pay - never-mind!