T3 / T4 test Results.: I wonder if anyone could... - Thyroid UK

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T3 / T4 test Results.

I wonder if anyone could explain my blood results. My GP (who is trying to help me) requested bloods but said they may not test and send results as FT3 should be requested by an Endo, so I paid for bloods myself just in case and also to speed the process. My bloods taken only 6 days apart, both under the same conditions (no Levo for 24 hours before, no food before and only water) are very different, why would this happen?

First set - TSH <0.005mlU/L (range 0.27-4.2) … FT3 5.51pmol/L (range 3.1-6.8) … Free Thyroxine 26.5 pmol/L (range 12-22) … Thyrogloglobulin antibodies 10.4 kU/L (range <115) … Thyroid Peroxide antibodies <9.0 klU/L (range <34).

second results, 6 days later _ TSH <0.30mu/L (0.35-4.94) … FT3 4.0 pmol/L (2.6-5.7) … Serum Free T4 (XaERr) 18.5 pmol/L (9-19.0) … Serum ferritin (XE24r) 34ug/L (15-200) … Serum vitamin D 85.0 nmol/L (71-200) … serum folate 17.2 ug/L (3-20) … serum vitamin B12 level 516 ng/L (180-640).

If anyone can explain or advise me on the above I would be very grateful. I will be seeing my GP next week and need to be able to understand the results and especially why they vary so much.

Many Thanks.

6 Replies


First of all, when the reference ranges are different, you have to work out what the percentage through range the result is and compare that, not the actual result.

First set -

TSH <0.005mlU/L (range 0.27-4.2) … suppressed

FT3 5.51pmol/L (range 3.1-6.8)65.14% through range

Free Thyroxine 26.5 pmol/L (range 12-22) … 145% of range

Thyrogloglobulin antibodies 10.4 kU/L (range <115) …

Thyroid Peroxide antibodies <9.0 klU/L (range <34).

The antibody results are low so are negative for autoimmune thyroid disease (Hashimoto's), although it is possible to have Hashi's without raised antibodies.

Second results, 6 days later _

TSH <0.30mu/L (0.35-4.94) … just below bottom of range

FT3 4.0 pmol/L (2.6-5.7) … 45.16% through range

Serum Free T4 (XaERr) 18.5 pmol/L (9-19.0) … 95% through range

So yes, the percentages are different. Both TSH results are low, both FT4 results are high, and there's a difference in the FT3, but if conditions were exactly the same there doesn't seem to be any obvious reason for it. However, you haven't said what time the bood was taken - if you can let us know the time of each test that may account for the difference in FT4 and FT3 because they both have a circadian rhythm and will vary throughout the day:


Serum ferritin (XE24r) 34ug/L (15-200) …

This is too low, recommended is half way through range (minimum of 70 for thyroid hormone to work properly). I was offered iron tablets when my ferritin was 39. I preferred to raise my level naturally. You can do this by eating liver regularly, maximum 200g per week due to it's high Vit A content, also liver pate, black pudding, and including lots of iron rich foods in your diet


Serum vitamin D 85.0 nmol/L (71-200) … = 34ng/ml

This is on the low side.

The Vit D Council recommends a level of 125nmol/L (50ng/ml) and the Vit D Society recommends a level of 100-150nmol/L (40-60ng/ml) and to reach the recommended level from your current level the Vit D Council suggests supplementing with 2,500iu D3 daily


Retest after 3 months.

When you've reached the recommended level then you'll need a maintenance dose to keep it there, which may be 2000iu daily, maybe more or less, maybe less in summer than winter, it's trial and error so it's recommended to retest once or twice a year to keep within the recommended range. You can do this with a private fingerprick blood spot test with an NHS lab which offers this test to the general public:


If Hashi's is present then for best absorption an oral spray is recommended or sublingual drops, if no Hashi's then good absorption is obtained from D3 softgels rather than tablets or capsules.

There are important cofactors needed when taking D3 as recommended by the Vit D Council -


D3 aids absorption of calcium from food and K2-MK7 directs the calcium to bones and teeth where it is needed and away from arteries and soft tissues where it can be deposited and cause problems such as hardening of the arteries, kidney stones, etc.

D3 and K2 are fat soluble so should be taken with the fattiest meal of the day, D3 four hours away from thyroid meds if taking tablets/capsules/softgels, no necessity if using an oral spray

Magnesium helps D3 to work. We need Magnesium so that the body utilises D3, it's required to convert Vit D into it's active form. So it's important we ensure we take magnesium when supplementing with D3.

Magnesium comes in different forms, check to see which would suit you best and as it's calming it's best taken in the evening, four hours away from thyroid meds if taking tablets/capsules, no necessity if using topical forms of magnesium.


Check out the other cofactors too (some of which can be obtained from food).

serum folate 17.2 ug/L (3-20) …

This is good.

serum vitamin B12 level 516 ng/L (180-640).

Not quite at the level recommended in the book, "Could it be B12?" by Sally M. Pacholok:

"We believe that the 'normal' serum B12 threshold needs to be raised from 200 pg/ml to at least 450 pg/ml because deficiencies begin to appear in the cerebrospinal fluid below 550".

"For brain and nervous system health and prevention of disease in older adults, serum B12 levels should be maintained near or above 1000 pg/ml."

It's possible to have a reasonable serum B12 level but a low Active B12 level. If you want to test Active B12 then Medichecks do a fingerprick test. If Active B12 is below 70 that suggests testing for B12 deficiency.

You can check for signs of B12 deficiency here:


If you have no signs then you could supplement with a good B Complex containing methylcobalamin (not cyanocobalamin) and methylfolate (not folic acid), although you don't need a high dose of methylfolate as your folate level is already good. You could consider Igennus Super B - 1 tablet.

Don't start all supplements at the same time. Start with one, leave it 1-2 weeks and if no adverse reaction then add the second one. Continue like this. If you have any reaction then you will know what caused it.

1 like

Thank you so much for explaining this. I had a total thyroidectomy and radio active iodine to cure thyroid cancer. The first blood test was 0940 the second 1120 in morning. I am having muscle and joint problems, no energy and loosing my hair. I think i need to lower my T4 and maybe take some T3 as this will prob drop when i lower T4. What do you think. Thank you So much for any advice.



You seem to need a high FT4 to get a reasonable amount of FT3 so your conversion could be better. However, good conversion can be helped by optimal nutrient levels, also by supplementing with selenium l-selenomethionine and zinc (some people prefer to test before supplementing).

As mentioned, ferritin needs to be at least 70 for thyroid hormone to work properly so you need to improve that.

Symptoms of low ferritin are mentioned in this article


Muscle and joint aches and pains can be low Vit D. Although your level isn't dire, you may need it higher so I'd supplement to get that to the recommended level.

Optimise all nutrient levels then see where your thyroid levels lie before considering T3.


I seem to have symptons of underactive thyroid but my levels seem to say opposite!


Two things come to mind

1) symptoms of low nutrient levels, particularly ferritin - check number 1 in the symptom list I linked to


2) you do, in fact, have Hashi's without the raised antibodies.

My guess at the moment is the first of these two options.


Thank you for your help.


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