Negative result for thyroid peroxidase antibodies tpoab . necessary to test my thyroglobulin antibodies tgab ?

Depends on: Depends on the disease condition you are trying to confirm or rule out. For example, you should get a tgab done also if grave's disease is suspected.

Anti-thyroglobulin: Studies have shown that 99% of patients with hashimoto's thyroiditis have anti-microsomal antibodies, whereas only about 1/3rd had anti-thyroglobulin antibodies. In addition, 10-20% of persons without thyroid problems have anti-throglobulin antibodies (tg-a). These persons are likely at higher risk for future problems and should be watched more closely however, testing for tg-a is not necessary.