Thyroid UK
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Taking levo before blood test

I am due a blood test in about 5 weeks. I have read here that you shouldn't take your levo for 24 hours prior to the test. Can someone tell me why that is? Surely it gives a false result if you don't take your meds? The doctor wants to see what your levels are while you are medicated, don't they, to see that the meds are working?

9 Replies

The meds are in your system so they can see you are taking them (as your results will improve).

If you take your meds just before getting your blood test then you will get a peak in your blood of T4. So the results look better than they are because of that.


Most doctors medicate according to the TSH and more or less ignore T4 or T3 (which they shouldn't). If you take medication before your blood tests it will lower your TSH and make it seem as if you're taken sufficient medication and that may not be the case. So instead of the doctor increasing your dose, he will either keep to it or may even lower your dose to detrimental affect on the patient's metabolism. Never allow the doctor to reduce your dose according to your TSH result, particularly if you are feeling well.

You take levo first thing with one glass of water and don't eat for around 1 hour so that food doesn't interfere with the uptake of levo.

If GP hasn't test B12, Vit D, iron, ferritin and folate as we are usually deficient and can cause problems too.


I have been on 100 thyroxine for nearly 2 years and although I didn't feel well my test results were always 'normal' - the joint pain was horrendous. GP had advised no repeat prescriptions for thyroxine until after my yearly test - results were as follows:-

FT4 - 10.3 (range 12 - 22)

FT3 - 3.0 (range 0.3 - 4.2)

TSH 7.78 (range 0.3 - 4.2)

GP phoned with my results and said he was increasing dosage to 125 thyroxine - when I asked for ranges he said I didn't need to concern myself as I was only slightly underactive but I then asked the receptionist at the surgery for results. Also my cholesterol results were as follows:-

Total cholesterol - 7.9

LDL - 5.0

HDL - 2.4

TChol/DHL - 3.3

Sorry for the long post but can anyone advise me what can have caused my thyroid to go so low despite treatment - cholesterol has always been high but am wondering if this will lower when my thyroid results improve as my GP is trying to get me on to statins straight away. He has advised retesting in 8 weeks.

Am thinking of getting retested with Blue Horizons Medicals after 6 weeks as they offer B12, folate testing etc. Amazingly after only 5 days taking 125 thyroxine the joint pains have almost disappeared. Could 5 days have made such a difference? GP said no and it must be 'just one of those things'.


No wonder he blooming well he phoned you and told you to increase your thyroid hormones. You were very undermedicated to have a TSH of 7.7. (you have included your ranges for thyroid hormones).

You only get a yearly blood test if you are stable on the medication and have no symptoms.

Please change your doctor as the present one has no clue and may cause more serious health problems. To say you are 'slightly' underactive is like slightly 'lying' if you are already taking levo where the aim is to have a TSH of around 1.

Don't let the following link worry you - in fact it tells the truth that if we aren't medicated to an optimum other illnesses can arise. Your cholesterol is high because your levo is too low for you. A TSH between the (range 0.3 - 4.2) is used for diagnosing a patient who has clinical symptoms, and if the reading is above 4.2 they are hypothyroid (although the BTA says to wait till 10 before medicating (never heard such rubbish) but most doctors would prescribe if around 5. If we are diagnosed as hypo and given medication the aim is for our TSH to go lower than 4.2 and usually we feel better around 1and some of us even lower.

We have to read and learn and we eventually know more than those who are supposed to be treating us.

Maybe your doctor would learn a thing or two by reading the link below:-

Also email and ask for a copy of Dr Toft's Pulse Online article and question 6 highlight and discuss with your GP a regime to reduce your TSH as suggested by Dr Toft.


Thank you so much for your reply - meant to say in my earlier post that when I had an increase to 125 thyroxine about 15 months ago I suffered from palpitations and therefore the GP reduced my dosage again. I am back at work today and although ankles and legs still swollen the constipation I was suffering from has gone and I generally am feeling a lot better. As I usually take my thyroxine around 10 pm each night when should I take my last dose when getting retested - if I take it the night before and have my blood test around 9 am next morning is it likely to give 'false result' - many thanks to all the people on these boards who are able to advise.


Miss your night dose and you can take it after your blood test. You can also take the night dose as well the same day. Research has shown than some feel better taking a night dose as their stomach is empty the whole night. 24 hours is a reasonable gap between levo and blood tests.

I had palpitations all the time on levo. When T3 was added it helped a lot. I now take T3 only. Palpitations don't always mean that we are taking too much thyroid hormones. It may be that we are sensitive to the fillers/binders but are not getting the sufficient hormones we may need.

1 like

Yes, five days of an increase can cause relief. Whenever, whatever dose we are on, if we begin to get clinical symptoms again that's when we need another blood test. Definitely change your GP and never listen to the word 'normal' when you feel anything but. If you have swelling you aren't on a decent dose of hormones for you.


No no no

if you take your meds in the 24 hours before the test your results will come up high and your gp will reduce your dose and you will be back to square one from whichnit takes months to recover


Blood tests only measure what's in the blood stream, not what is working at cellular level, ergo if you take meds before a blood test you generally have a false result.


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