I have been feeling very tired for quite some time. Had blood test and my T4 had dropped to 17. My T4 needs to be about 21 for me to feel well . Doctor said I could increase up to 125 in two stages . Took extra 12.5 mcg and it didn,t make any difference so have just gone up to extra 25mcg. Just wondering , does T4 go lower with age as I am now 71.Last year had a full bloods done and I thought one or two things were in the bottom of range. Doctor said it was O.K.I am thinking of asking for another full blood test and if they say no maybe I should get a private one.