Response

Editor – Many thanks for the authors interest in our review. We fully agree with the several diagnostic pitfalls which need to be kept in mind while considering the diagnosis of vitamin B₁₂ deficiency and pernicious anaemia.

However, there are certain issues which we need to consider in this scenario. Firstly, performing serum methyl malonic acid and plasma homocysteine levels as routine work-up for vitamin B₁₂ deficiency is not common practice and also not available in many laboratories in the UK. The other issue which is becoming more common is considering serum B₁₂ testing as part of ‘routine blood tests’ without adequate thought into the clinical situation. This can lead to problems like the ordering physician overlooking vitamin deficiency as still a possibility for the patient's symptoms when normal serum B₁₂ levels are reported. Ideally in such cases, specialised tests like methyl malonic acid and serum homocysteine need to be performed. On the other hand, routine B₁₂ testing can identify several patients as having levels slightly lower than the normal range and are labelled as having B₁₂ deficiency. These patients are sometimes given life-long intramuscular B₁₂ replacement which may have been entirely unnecessary.

The author also states the importance of blood film and bone marrow examination in selected situations. We again agree with the fact that blood film examination should be an essential part of the work-up for B₁₂ deficiency, but don't think bone marrow examination is appropriate due to the fact that it is invasive and should only be done if the suspicion is still strong despite normal investigations obtained from blood samples.

Since the publication of the review, we have had several correspondences on how many physicians do not consider B₁₂ deficiency as the cause of symptoms in many individuals with varied problems, especially neurological symptoms. We have not been able to respond to all these individuals but do acknowledge the fact that missing the diagnosis of B₁₂ deficiency is quite widespread. We exhort the doctors to consider this diagnosis in patients with neurological symptoms and unexplained extreme tiredness among others, and not just macrocytosis and anaemia. In such cases, the appropriate investigations, including specialised tests in some cases, should be performed to exclude B₁₂ deficiency as the cause.