can't really add much to the advice you have been given on the TUK forum.
Low TSH would be indicative of hyperthyroidism but if that was the case then your T4 would be above range - so as said on TUK -more likely to be a deficiency that is affecting your results.
The range above for Ferritin is wrong - you've accidentally duplicated the range for folate - but 11 is likely to be a low measure - so indicative of iron deficiency.
full blood count and iron panel probably needed to help clarify.
being folate deficient and iron deficient (assuming your diet isn't total rubbish) means that you probably have an absorption problem such as PA/coeliacs/h pylori infection.
PA is the most common cause of B12 deficiency - its an auto-immune condition.
Your B12 is in the normal range - low in that range but still in range - you may or may not be deficient - serum B12 isn't a good test to use as a single measure as it will miss 25% who are B12 deficient but will also pick up 5% who aren't B12 deficient.
being both folate and iron deficient points to an absorption problem and makes the chances that you also have a problem absorbing B12 higher- so levels will fall over time until they are eventually below the normal range but you could be deficient now.
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