Fasting for blood test.

[Sunnydevon]

I’ve never fasted for blood test before but due to taking advice from the lovely people on this forum I am today. Will it make my results accurate or make them look like I’m more Hypo? Just reading over other posts and it’s confused me.

[bantam12]

I don't fast for thyroid bloods, the times I have fasted for other tests my thyroid results haven't changed.

[Aurealis]

As long as you also take your morning dose after the test, it will avoid you getting a false low TSH which leads GPs to wrongly reduce dose. It also provides a more stable FT3 FT4 levels which enable you to get a result which does not just reflect the time since your last dose and the test. My tests do seem to different if I fast.

[greygoose in reply to Aurealis]

Actually, taking your dose before the test doesn't affect the TSH, because it doesn't move that quickly. But, it will give you a false high FT4.

Fasting over-night is said to give a higher TSH, but opinions are divided. But, you do need to leave 24 hours between your last dose of levo, and 12 hours for T3, and the blood draw.

TSH is highest early in the morning, and drops throughout the day. So, having the test early makes you look more hypo, and as doctors only tend to look at the TSH, it increases your chances of diagnosis, or getting an increase in dose.

[Sunnydevon in reply to greygoose]

Thank you.