More on Vitamin B12: Diagnosis and Treatment

My last column was on vitamin B12, also known as Cobalamin. Some of my colleagues said that I took a very simplistic approach to diagnosis and treatment of vitamin B12 deficiency. There is more to it than what my column implied.

In this column I will elaborate on the following two points: diagnosis and oral vs. injection treatment of B12 deficiency.

Is blood test a good way of confirming the diagnosis of B12 deficiency?

I discussed this point with Dr. Michael O’Connor, Medical Director of the Medicine Hat Regional Hospital Laboratories. He said there is a difference between the very common asymptomatic B12 deficiency and the much less common symptomatic and clinically apparent B12 deficiency. He says interpretation of low B12 result is hugely dependent on the clinical situation of that individual patient.

If the patient has symptoms of B12 deficiency (anaemia, neurological and psychiatric problems) and the blood results shows B12 to be low then the diagnosis of B12 deficiency is easy to make. If an individual has no symptoms then there is probably no role for screening for B12 deficiency, says Dr. O’Connor.

The process is difficult because there is lack of a diagnostic gold standard among the many available tests, there are too many patients with sub-clinical deficiency and there is decreased availability of reliable tests to identify the causes of a patient’s cobalamin deficiency, says an article in Hematology.

How to treat B12 deficiency: by oral pills or monthly injections?

I received the following information from the Medicine Hat Regional Hospital Pharmacy.

Either oral or injection formulations are effective for treating B12 deficiency.

The main mechanism of B12 absorption is via its binding of intrinsic factor in the stomach and its subsequent absorption in the intestine. Approximately 60 per cent of cobalamin is absorbed by this system. A secondary mechanism of its absorption does not require intrinsic factor and involves passive diffusion across the intestinal wall. When given orally only one per cent of a dose will be absorbed by this mechanism.

The daily requirement of cobalamin is 2-3mcg. Dosing with intramuscular or deep subcutaneous injections to treat deficiency involves 100mcg daily for five to 10 days, then 100-200mcg monthly until levels are normalized followed by 100mcg monthly for maintenance.

High oral doses in the range of 1000 to 2000mcg daily are just as effective for treating deficiency due to the secondary mechanism of absorption. Cobalamin can also be administered sublingually both safe and effectively (2000mcg). The benefit to sublingual cobalamin vs. oral is not well defined.

There are disadvantages to give patients regular injections of B12. They are: pain at the injection site, injection site reactions, inconvenience and higher cost due to the need for a health professional to administer the injection.

Despite these disadvantages injection treatment is still preferred for those patients who are unable to take medications orally, those who experience severe diarrhea or vomiting, those with compliance issues to a daily dosage regimen, as well as those with neurological symptoms.

Oral and sublingual cobalamin have no evidence of toxicity when used at high doses, are cost effective, less burdensome to the patient and are equally as efficacious when used at the appropriate doses as compared to injection dosage forms. The only disadvantage to choosing an oral or sublingual regimen is the potential for adherence issues. Hence oral cobalamin is an excellent option for treatment and prevention of mild to moderate cobalamin deficiency.

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One Reply to “More on Vitamin B12: Diagnosis and Treatment”

  1. I have a mutation from my stomach or intestines that doesn’t absorb vitamin B12. Where can I get genetic testing done?

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