Pernicious Anaemia Society
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Recent B12 blood test results. Do I need to supplement?

Hi there,

I recently had my Vit B12 tested as I have an under active thyroid and it is suggested we check B12 also. My results are:

423 pg/ml (200-1100)

I have had previous B12 tests but they were actually better, at around the 500 mark. I don't understand why it has gone down as my thyroid health is actually better.

Any advice is greatly appreciated.


6 Replies

Yes you should supplement with B12. As we become older absorption is impaired. You need your level to be close to the TOP of the range. Anything below 500 can cause neurological symptoms....

Good videos and excellent information. I would suggest 5000mcg of B12 Methylcobalamin by JARROW obtainable on-line. You cannot overdose as it is excreted. You need a GOOD B Complex as well to keep all the B's in balance....

Only 20% of the B12 in your blood can be utilised at a cellular level where it is needed....


...once taking supplements further testing is of little value. Couldn't work the Edit button :-)


Thats great Marz. thanks for the link!


"423 pg/ml (200-1100)"

People can be symptomatic for B12 deficiency at these levels. Has your GP talked to you about why your B12 levels have dropped?

Are you symptomatic for B12 deficiency?


If you are, the PAS are helpful to talk to. You can leave a message.

Head office: 01656 769 717

Recent articles suggest that symptomatic patients should be treated even if blood results are normal range.

Google the "BCSH Cobalamin and Folate Guidelines" . Have a look at page 29, a diagnosis flowchart.

Useful books

Could It Be B12 by Sally Pacholok

Pernicious Anaemia : The forgotten Disease by Martyn Hooper

Living with pernicious Anaemia by martyn Hooper

As marz says once you supplement with B12 it will affect your B12 test results.

There are IFA (Intrinsic Factor Antibody ) tests, MMA, Homocysteine and Active B12 tests. these can be done privately if your GP does not offer them.


The drop is an indicator that you have an absorption problem - and there are many - PA (autoimmune response) is one, drug interactions are another and lowering of stomach acid as you get older is yet another one.

Most of your B12 is absorped in the ileum - 99% - so it is possible to flood the gut with B12 and for enough of it to get through.

B12 is stored in the liver and then released back into the blood stream through bile into the ileum so it can take a very long time for an absorption problem to manifest itself in a B12 deficiency ... though it does tend to accelerate as once the ileum absorption rate has dropped your ability to recycle any excess also disappears.

As Marz and Sleepybunny indicate the serum B12 test is not a particularly good indicator of whether there is a deficiency or not - partly because it looks at all B12 not just active forms and partly because it tells you absolutely nothing about what is happening at the cellular level. Recommendation of BCSH is to treat on basis of symptoms not on test results, particularly where there are neurological problems.

If you have an absorption problem then you need to be taking at least 100x the RDA - generally recommended about 1000mcg - 5000 mcg a day (1=5mg), so most over the counter medications aren't going to come anywhere near that.

You also need to make sure that your folate levels (B9) are good - upper half of range - as the body needs folate to process B12 ... also needs B6 for some functions, but the body can also convert B9 to B6 so that is less of an issue. If you can do this through diet that is best, however, if you have an absorption problem then that may also be affecting other vitamins.

At the very least your GP should continue to monitor B12 levels and if they continue to decline think about treating you.

1 like

Please contact the Pernicious Anemia Society. They have all the information needed. Martyn Hooper is a godsend to sufferers like myself. Finally, someone who will listen that understands. He is the Chairman of the Pernicious Anemia society and has written a couple of useful books which are available on ebay. Hope you get your health problems sorted soon.

Kind regards,



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