Normal tsh..t4 is high .retake blood test again still high ..retake it again ..now its normal. why is that?

Lab values vary: Lab values can vary (assuming there has been no change in a patient's status nor medications). That is why lab results are "just numbers", and one should see the doctor for an interpretation of the numbers. Sometimes, 3 tests are done to see if 2 of the 3 results will match closely. A doctor may know if certain lab locations or lab companies tend to "run high" or "run low" on their results.