Loose bowel motions may be due to an infection (gastroenteritis) but if the symptoms persist for more than 3 weeks then other conditions need to be considered. Sometimes the problem is......

B12 Deficiency

This picture shows changes to white blood cells in untreated perncious anaemia

B12 Deficiency and Pernicious Anaemia



Historical Perspective

  • The presentation of B12 deficiency is dramatically different from 30 years ago.
  • The reason for this is the routine availability of testing of serum B12 concentration.  In the past the condition was only diagnosed when there were symptoms of tiredness, loss of concentration, irritability and numbness and tingling in the arms and legs.  Examination showed evidence of nerve damage. Blood tests showed an anaemia and there were also changes in the bone marrow. This condition did not respond to iron tablets.
  • Before B12 replacement treatment was available the condition became worse or could lead to death – this led to the term pernicious anaemia.




How reliable is the blood test for B12?

  • Blood levels of B12 (serum levels) are now tested very frequently.
    • There can be problems with “routine” or frequent testing.
    • It is difficult to define the appropriate normal values in a population.
    • Sometimes a value just below the normal range is not really important and can be ignored.
  • Blood tests only tell part of the story.
    • B12 is stored in the liver - only a small part in the blood.
    • There is actually enough B12 stored in the liver to last for at least 3 years.
    • The blood levels does not always accurately reflect the levels of stored B12.



Does a low B12 level in the blood really matter?

  • Most people with a low B12 will have no changes in body function.
    • If there is anaemia or changes in the blood count then it is obvious that the low B12 is significant and that replacement treatment should be given.
    • There have been several proposals for tests that can show if the B12 is having a functional difference in the body’s metabolism but these tests are not routinely available and may not be that accurate.
  • Most people have tiredness as the major symptom.
    • It is always going to be difficult to know if this symptom is related to the low B12 result.
    • If the level is only borderline low the response to B12 injections may be disappointing.
  • Problems with memory or concentration or numbness in arms or legs are likely to improve but these changes only occur with more severe deficiency – in this situation there are usually also changes in the blood count and the size of the red blood cells.



How should B12 be given?

  • B12 replacement is given by intramuscular injection.
    • Initially 1000ug every week for 4-6 weeks.
    • A maintenance dose of 1000ug every 3 months is recommended. This dose will give B12 levels well above the daily requirements.
  • Oral absorption is very poor and tablets are not recommended.
  • Treatment needs to be life-long if the low B12 is due to pernicious anaemia or due to previous small bowel surgery.
  • Milder reductions in B12, without any obvious cause just require a course of injections   - maybe 3 injections over 3 months then follow-up yearly to see if there is any recurrence


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