Thyroid UK
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Optimal ferritin levels: what unit of measurement?

I've often seen it mentioned that for people with hypothyroidism their ferritin level should be at least 70. But is that 70 ng/ml or 70 pmol/l? They are substantially different: 70 ng/ml is 157 pmol/l; 70 pmol/l is 31 ng/ml.

For example, my private blood work was measured in ng/ml and came back as 4, my NHS bloods were done a week later, the result 8 pmol/l. Which 70 should I be shooting for?

8 Replies

I would suggest aiming to get your ferritin to about mid range or a little higher. The units are irrelevant then.


It would be helpful if you gave the results you have along with the reference ranges.


First test 4 ng/ml (15-200), second test don't know the ranges.


I would have thought your optimal level would have been approximately 100 ng/ml on the basis of this range.

Your level is dreadful and you must feel awful. What has your doctor suggested doing about it?

I would have thought, in an ideal world, you would need an urgent referral to haematology and being given an iron infusion. But I don't know how the NHS deals with extremely low iron, my ferritin never got as low as yours.


I've been prescribed 305 mg ferrous fumarate daily, which I take just before bed together with 1000 mg vitamin c and 400 mg lithium chaser :)

I only discovered my ferritin levels were low because I paid for private blood tests when on holiday in France last month (after learning about the importance of this from the HU TUK community). My FBC had previously always come back 'within range' so no warning bells sounded. I just felt a bit tired and my fingers went blue at the tips when I ran but nothing too bad. Ironically, I feel worse now that I'm taking the iron.

I'm currently on a voyage of discovery about the effects of low stomach acid, which may cause laryngopharyngeal reflux (so-called 'silent reflux'); this might explain my many ENT issues (including perpetual postnasal drip and mucus that I just can't seem to shift from my throat). Low stomach acid also impairs absorption of nutrients, which may explain how things got so bad overall. Dammit, hagnanny, I just want to feel well!


I had a ferritin level of 21 ug/L (range : 13 - 150). It was an NHS test done in Spring 2013. I managed to persuade my doctor to prescribe iron for me, which she did very, very reluctantly. Quite by accident, when I got the prescription from the pharmacist, I discovered that I didn't need a prescription I could buy reasonable strength ferrous fumarate without one.

So, my prescription was for 210mg ferrous fumarate to be taken 3 times per day, and I was prescribed enough for 8 weeks. The pills are available from some pharmacies without prescription. Boots insist on a prescription but Lloyds don't. Shop around, one box should cost roughly £4. One box contains 84 tablets - enough for 3 per day for 28 days.

After my prescription supplies ran out I started buying my own. Of course, as a result, I've had to pay for my own blood testing too, but not having to ask permission from my doctor to feel better has made it all worthwhile as far as I'm concerned.

I've had a couple of breaks from taking the iron to see how I feel, but I've gone back on it again within 2 or 3 weeks each time. I'm still taking iron now. It's been about 15 months since I started. My levels of ferritin, serum iron, haemoglobin, red blood cell count, haematocrit, and all the other iron and full blood count levels are finally getting close to a sensible part of the range, although my ferritin is still only about 40, when mid-range would be about 70.

And the good news is that I can now get upstairs without having to crawl, with much less pain, and without feeling like I will faint at the top. But, of course, my doctor would say those symptoms were all in my head because my ferritin was always in range...

You might find the dose of iron I took is more successful for you than the whopping single dose you've been prescribed.

The info on iron supplements that your doctor reads in the British National Formulary can be found here :

The link refers to ferrous sulphate as being the standard prescription but it is very poorly tolerated, so avoid it like the plague.


Interestingly my pharmacist looked in the BNF and told me that 305 mg is the maintenance dose, not the therapeutic dose! But the nurse practitioner that I saw last week told me that increasing the dose was pointless as there was only so much iron that could be absorbed; I think she's probably got a point!


If you took a smaller dose but took it more times a day it might increase your absorption. Just a thought...


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