Thyroid UK
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I have recently been diagnosed with an underactive thyroid and put on a starting dose of 50. I have blood tests in a couple of months to check levels again and assume my dose will increase.

My test results show serum free T4 level of 7.1 pmol/L (7.5 - 21.1) and Serum TSH level of 27.05 miu/L (0.34 - 5.6) but I have no idea what this means and whether my thyroid is very underactive (if that is a thing). I would appreciate any advice and also any thoughts of when I might notice the impact of the medicine.

Thank you in advance

14 Replies

Welcome to the forum, Lloyd123.

TSH 27 is high. Someone with a healthy thyroid would expect to have TSH around 1.0 with FT4 around 16.

The goal of Levothyroxine is to restore the patient to euthyroid status. For most patients that will be when TSH is 1.0 or lower with FT4 in the upper range. FT4 needs to be in the upper range in order that sufficient T3 is converted. Read Treatment Options in

For maximum absorption Levothyroxine should be taken with water 1 hour before, or 2 hours after, food and drink, 2 hours away from other medication and supplements, and 4 hours away from calcium, iron, vitamin D supplements and oestrogen.

It takes 7-10 days for Levothyroxine to be absorbed before it starts working and it will take up to six weeks to feel the full impact of the dose. Symptoms may lag behind good biochemistry by several months.

You should have a follow up thyroid test 6-8 weeks after starting Levothyroxine. Arrange an early morning and fasting (water only) blood draw when TSH is highest, and take Levothyroxine after your blood draw.


Thank you! It sounds like my TSH reading is very high, should I be concerned/doing anything other than taking medicine?

My blood tests will be 8 weeks after the diagnosis, I will follow the advice regarding fasting. They are in the morning but not early morning (I think about 10:30am).

If my levels are so different to the normal levels am I likely to see any impact when still on a starter dose?

Sorry about all the questions this is new to me so not sure what I should expect.

Thank you again!



TSH isn't that high, some members are diagnosed with TSH >100 and one member with TSH >240. Symptoms don't necessarily correlate with how high TSH is. Patients diagnosed with TSH >20 often respond quicker and better than those diagnosed at lower levels but I wouldn't expect much improvement in symptoms until TSH is around 1.0.

You should be cautious for a while while driving because research has shown that having TSH >20 can impair driving reactions more than being over the drink drive limit.

FT4 will rise and TSH will drop in response to 50mcg but I think that you will need a dose increase after your blood test. Thyroid replacement has to be introduced gradually to avoid causing an adrenal crisis. Levothyroxine is usually increased in 25mcg increments every 6-8 weeks with blood tests 6-8 weeks later to monitor response.

Hypothyroid patients are often low/deficient in ferritin, vitamin D, B12 and folate which can cause symptoms similar to hypothyroid symptoms so it may be worth asking your GP to do blood tests when you have your next thyroid blood test.


Clutter, do you by any chance have a link to the driving with TSH >20 research? I know I've seen this somewhere but can't find it now.


Thanks Clutter. Google also came up with and

Would be useful to have this on the TUK website in case anyone needs something official for some reason.

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Thank you! Sounds like I shouldn't worry too much and need more patience. My symptoms are not that bad compared with some other members, I went to the doctor because I was feeling tired and couldn't lose weight but assumed I was just a bit run down and eating too many biscuits!

The doctor hadn't mentioned anything about driving but I will be cautious from now on. It wouldn't be very easy for me to give up driving completely but will try to avoid when possible.


Your GP won't.

Remember they are "General Practitioners" so unless they have it themselves or a close family member they will only know what is in their guidelines or told to them by a specialist.

Be aware the guidelines aren't helpful for a minority of patients though most people are fine once they are on the correct levo dose.


Lloyd123, The majority of doctors don't really understand the impact that hypothyroidism has on cognitive function. And hypothyroidism is not a notifiable condition with respect to the DVLA (because the problem is considered to be reversible with appropriate medication). I have wondered how well it might stand up in court if it had to be put to the test.

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Good morning! I spoke to the doctors receptionist week before last to see if my blood tests have come back. She confirmed they had and have come back normal so I need a repeat prescription of 50mcg. I have asked for a copy of the results but haven't had time to collect them but wanted to ask whether it is possible for 50mcg to be a sufficient dose. I do still have some days where I feel exhausted but I do have more days feeling fine (I also have 3 children under 6, am changing job and moving house which could explain the tiredness). I haven't been on Levothyroxine that long so not sure whether a bit early to feel the full impact. As the tests are normal they have said test again in a year. Do you think I should ask for it sooner?

Thanks in advance.


I have now collected my test results which say Serum TSH level 0.90 may/L [0.34 - 5.6]. I have a doctors appointment next week and looking for some advice as to whether I should be asking them anything or request blood tests again in a couple of months. As I mentioned in my previous post I still feel tired but there might be other reasons for that. It looks like from my results that 50 might be a high enough dose?

Thank you in advance for any help!


What time of day did you have your blood taken?

How long a gap did you leave between previous dose of levo and the blood draw for testing?

Assuming your blood draw was done early in the morning, did you fast overnight and before the blood draw (apart from water)?


I had my blood test at 8:10am. I usually take Levo between 7:30am and 8am but I took it after my blood test. I hadn't eaten anything since my evening meal at approx 8pm.




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