the doctor is concerned not only about you but also his/her liability in requiring these tests. If I were your doctor and you absolutely refused tests I deemed as essential I would no longer prescribe you the medication, reluctantly
However I might suggest you discuss your anxiety over such testing and see if the interval between these tests can be lengthened gradually since you say the test results so far have all been positive. Yet if the drug you are taking has toxic qualities and is potentially dangerous surely some regularly testing is needed, period.