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.
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
“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