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Pernicious Anaemia Society
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B12 after loading dose

My B-12 levels were below 100 and I did one week of B12 injections. On my last day of the loading dose, I had an appt with my hematologist and he did a bunch of blood work. I just got my test results and my b12 was 6971. I had a weird reaction to the injections in that I was exhausted the whole week and felt terrible... Is it normal to have such high levels? Somehow I thought it would take a lot more to even out my levels. And with all that B12 I would think I'd have energy? Any other experiences?

3 Replies

Hi TenilleMarie fortunately you cannot "overdose" on B12 as any excess is excreted via your urine. Taking a serum B12 test so soon after an injection was bound to come out high.

The injections are not an overnight cure and it will take some time before improvement - indeed you may even feel they are getting worse before they get better as the B12 starts repairing the damage done to your nerves caused by the deficiency.

Do you know what your Folate level is as this and the B12 helps Iron to make red blood cells and a deficiency will cause this not to work properly.


I'm on 2-3 mg of folic acid daily so my folate levels are on the low side of "normal" . I'm on methotrexate for autoimmune issues so the folic acid is to even out the side effects. I'm wondering if my body doesn't absorb b12 into my muscles/tissues but keeps it in the blood stream. I have another hematology appt in 3 weeks so we'll see what they say. I have hemachromatosis and my iron and ferritin are high again so I have regular phlebotomy again.

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Immediately after loading shots you will have very high B12 levels. As Clive says filling your blood up with B12 doesn't necessarily resolve problems over night - if you had macrocytic anaemia (red blood cells slightly rounder and larger than normal) then that will take a while to correct and if that is why you are tired.

Most of the B12 currently in your blood will just be removed by the kidneys and pass out in your urine - but there is a lot of variation in how long that takes.

methotrexate certainly plays havoc with folate - may be that even 2-3mg isn't enough and without folate you aren't going to be able to use B12 fully as the two are used together for a number of key processes - including the production of red blood cells.


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