Testing B12 during treatment

We often hear of individual doctors, and some nurses, who believe that the patient with Pernicious Anaemia should have his or her B12 levels monitored when they are being treated with replacement therapy injections of B12. The main reason why this happens is that the patient will return to their health professional and ask for more frequent injections because they are experiencing a return of their symptoms. The doctor will then order a serum B12 test that will invariably show that the patient has high levels of B12 – well he or she would, as they have, after all, been receiving injections of the vitamin. Based on this high level treatment is sometimes erroneously reduced or even stopped.

Serum B12 levels cannot be used to determine the maintenance treatment frequency as the values will not give an accurate picture of the effect of the treatment. Rather, the patient’s symptoms, and when they return, should be the only basis for developing an individual treatment plan for the patient. There is no correlation between the serum B12 value and the symptoms experienced by patients.

Another reason why doctors try to monitor the patient’s B12 status is because they erroneously believe that the patient can overdose on B12. Because there is no danger of overdosing vitamin B12, treatment should be based on the individual needs of each patient in order to attain optimal recovery.
Whilst some patients manage their condition well on two-monthly or even three-monthly injections, a large number of patients experience a return of their symptoms before their injection is due. It isn’t clear why some patients need much more injections than others in order to feel well and prevent a recurrence of the symptoms, but research into this is underway.

Current Guidelines

Measuring cobalamin levels is unhelpful as levels increase with treatment regardless of how effective it is, and retesting is not usually required.

NICE Clinical Knowledge Summaries Management of anaemia – vitamin B12 and folate deficiency
based on expert opinion in a narrative review Vitamin B12 deficiency [Hunt, 2014] the British Medical Journal (BMJ) best practice guide Folate deficiency [BMJ, 2017a].

Maintenance treatment for patients presenting without neurological deficit is with hydroxocobalamin 1000 lg i.m. every 2-3 months. Those with initial neurological deficit should receive hydroxocobalamin 1000 lg i.m. every 2 months.
No further testing for cobalamin levels is required.

Guidelines for the diagnosis and treatment of cobalamin and folate disorders
British Society for Haematology Guideline

Cobalamin and holo-transcobalamin II levels are uninformative because they rise with cobalamin influx regardless of therapeutic effectiveness”.

How I treat cobalamin (vitamin B12) deficiency,  R. Carmel; Blood. 2008 Sep 15; 112(6): 2214–2221. doi: 10.1182/blood-2008-03-040253

“During vitamin B12 injections, transcobalamin en haptocorrin are fully saturated with vitamin B12. Therefore, serum and Active B12 values cannot be used to ascertain the effect of treatment.”

Approaches to vitamin B12 deficiency  Henk Russcher, Sandra G. Heil, Lennert Slobbe en Jan Lindemans; Nederlands Tijdschrift Voor Geneeskunde, 01 Jan 2012, 156(1):A3595

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