Tsh higher t4 staying the same ?

If you only had TSH and Free T4 measured there are so many factors which could change one but not the other.

1) The time of day the blood was drawn.

2) How recently before the blood draw you took thyroid meds.

3) How recently you ate or drank.

4) Your Free T3 level may have changed.

5) If you have been taking non-thyroid meds which affect your thyroid.

6) If you've been under prolonged stress or have managed to reduce stress, your cortisol and/or adrenaline levels may have changed. Cortisol and adrenaline have knock-on effects on your thyroid production, conversion and use by the body.

7) Supplements - starting or stopping any - could have an effect.

8) Your reverse T3 levels may have changed.

9) You may have had a virus, just recovering from one, or may just be developing one.

10) You may have higher or lower levels of antibodies.

11) Whereabouts in your menstrual cycle you are.

I've no doubt there are other things which could change your levels. But all the NHS cares about is your TSH, and occasionally your Free T4. The other factors rarely cross a doctor's mind.