NHS use a range of 7.86 - 14.41 pmol/L when measuring t4. However, every time I've had a private test they use much higher reference ranges of roughly 12-22 pmol/L. Even weirder, my t4 always comes back much lower when NHS tested, and higher when privately. Therefore, it always comes back within range.
I know different labs use different ones, but my previous 5 tests have been:
15.5 (private, most recent)
8.9 (NHS)
9 (NHS)
9.5 (NHS)
9.4 (NHS)
16.2 (private)
15.8 (private, oldest)
They're the same unit of pmol/L. Just confused as my most recent private test of 15.5 would be classed as too high by the NHS range, and my previous 4 NHS tests would be classed as too low by the private range. Am i missing something?!
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katyy94x
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Hello, yep all done around 7:30am having fasted. None of these tests were done whilst taking levothyroxine, but i have literally just started it. Weirdly, my TSH was highest it's been when my t4 was 15.5. What might cause my t4 to naturally have improved whilst my TSH has gotten worse?
Waiting for my GP to come back to me about my vitamin levels at the moment.
Serum ferritin level is the biochemical test, which most reliably correlates with relative total body iron stores. In all people, a serum ferritin level of less than 30 micrograms/L confirms the diagnosis of iron deficiency.
Never supplement iron without doing full iron panel test for anaemia first and retest 3-4 times a year if self supplementing.
It’s possible to have low ferritin but high iron
Test early morning, only water to drink between waking and test. Avoid high iron rich dinner night before test
Eating iron rich foods like liver or liver pate once a week plus other red meat, pumpkin seeds and dark chocolate, plus daily orange juice or other vitamin C rich drink can help improve iron absorption
This is interesting because I have noticed that many patients with Hashimoto’s disease and hypothyroidism, start to feel worse when their ferritin drops below 80 and usually there is hair loss when it drops below 50.
Really interesting talk on YouTube, link in reply by Humanbean discussing iron deficiency and weight gain and towards end how inflammation can also be an issue
Thank you for your incredible patience while you have been awaiting the outcome of our ferritin reference range review. We conducted this with Inuvi lab, which has now changed the reference ranges to the following:
Females 18 ≤ age < 40. 30 to 180
Females 40 ≤ age < 50. 30 to 207
Females 50 ≤ age < 60. 30 to 264l
Females Age ≥ 60. 30 to 332
Males 18 ≤ age < 40 30 to 442
Males Age ≥ 40 30 to 518
The lower limits of 30 are by the NICE threshold of <30 for iron deficiency. Our review of Medichecks data has determined the upper limits. This retrospective study used a large dataset of blood test results from 25,425 healthy participants aged 18 to 97 over seven years. This is the most extensive study on ferritin reference ranges, and we hope to achieve journal publication so that these ranges can be applied more widely.
Hi there SlowDragon Ive seen a few posts lately quoting the CKS ferritin reference range <30. I find it a bit misleading. I think we also need to say that first of all, something on your FBC must be out of range, for instance haemoglobin. If it is, AND if ferritin is below 30, then it is a confirmation of iron deficiency anemia. Ferritin <30, on its own, does not indicate iron deficiency anemia in the NHS. I know you understand the CKS and the contact of ferritin, but not everyone will, so im adding it here.
Whatever the rest of the NHS says and believes, the NICE CKS seems to be absolutely unambiguous:
NICE
Clinical Knowledge Summary > Anaemia - iron deficiency
Last revised in September 2023
Serum ferritin level is the biochemical test that most reliably correlates with relative total body iron stores. In all people, a serum ferritin level of less than 30 micrograms/L confirms the diagnosis of iron deficiency.
helvella Hi there. Yes I know that with a glance it appears to say that about ferritin. If you read it from the top, in the order it is written, it clearly states
"Anaemia is defined as a haemoglobin (Hb) level two standard deviations below the normal for age and sex.
In men aged over 15 years — Hb below 130 g/L.
In non-pregnant women aged over 15 years — Hb below 120 g/L.
In children aged 12–14 years — Hb below 120 g/L.
In pregnant women — Hb below 110 g/L throughout pregnancy. An Hb level of 110 g/L or more appears adequate in the first trimester, and a level of 105 g/L appears adequate in the second and third trimesters.
Postpartum — below 100 g/L."
Then it goes on to say that diagnosis is confirmed (following the Hb result) by a ferretin<30.
The reason is says "in all people" is because the hb levels are differentiated for sex and pregnancy status, but ferretin is not.
NHS follows Nice guidance, so I was not meaning to differentiate NHS from cks. The cks are from nice, and nice guides NHS practice.
I'm 100% certain of what I'm saying. Read it again, you may see my point. I misunderstood it the first few times I read it. I have verified this with scientists and clinicians. My intention of correcting here is to prevent people from going to their GP with the wrong information and being disappointed.
I'm 💯 with you about using ferretin as a guide and getting it up to help with some symptoms.We know that. But unfortunately it doesn't change what CKS says. Unfortunately. And imagine relying on the information here, going to a GP, and being shot down. We all know how demoralising that is. And unfortunately the GP would be right to look for poor Hb result before considering ferritin.
I was very excited when I first read the cks. I thought... finally, common sense! But, no 😭
With serum B12 result below 500, (Or active B12 below 70) recommended to be taking a separate B12 supplement
A week later add a separate vitamin B Complex
Then once your serum B12 is over 500 (or Active B12 level has reached 70), you may be able to reduce then stop the B12 and just carry on with the B Complex.
If Vegetarian or vegan likely to need ongoing separate B12 few times a week
Thorne Basic B recommended vitamin B complex that contains folate, but they are large capsules. (You can tip powder out if can’t swallow capsule) Thorne can be difficult to find at reasonable price, should be around £20-£25. iherb.com often have in stock. Or try ebay
IMPORTANT......If you are taking vitamin B complex, or any supplements containing biotin, remember to stop these 7 days before ALL BLOOD TESTS , as biotin can falsely affect test results
In week before blood test, when you stop vitamin B complex, you might want to consider taking a separate folate supplement (eg Jarrow methyl folate 400mcg) and continue separate B12
Post discussing how biotin can affect test results
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Never delay seeking advice or dialling emergency services because of something that you have read on HealthUnlocked.
NHS Bristol changed their T4 range to 7.9 – 14.4 pmol/L
Improving T4 to T3 conversion 
Thoughts on thyroid results?
Medichecks results
please could you check these thyroid results please.
