HypoThyroidsm. The best for a tsh test?

I have a major concern about the way Hypothroidism is identifed in a pateint and also the range used. What I have noticed is TSH levels are usually very high, if the blood samples are given on fasting and in morning. TSH levels are low in afternoon or much lower in the evening. However, when a doctor is consulted, he or she never asks you the time you have done the test. Also they use the same range for all these times. I don't think this really makes sense. I think if the TSH is a hormone which in all human beings in supposed to be high in the morning, then the range used for a test done in the morning should be different from that done in other part of the day. Which time is considered the best for a tsh test? Also why doctors never tell their patients to do the test at the same time for all followups to see the progress of treatments. I really feel thyroid being now one of the most common diseases identified globally, there should be more research done on this issue.