Methods This retrospective study reviewed the electronic medical records of 192 patients initiated on intramuscular vitamin B12 injections.
Results Only 12 patients had objectively documented hematologic responses: decrease of mean corpuscular volume by greater than or equal to 5 fL with stable or improved hemoglobin. Another 5 patients had equivocal hematologic responses. There was one plausible neurologic response. Thus, only 18 (9.4%) of 192 patients had data supportive of a clinical response. In these 18 patients, the baseline serum B12 level was less than or equal to 107 pg/mL; only 3 patients also had a baseline serum methylmalonic acid level, which was greater than or equal to 1.29 μmol/L in all 3 patients.
Conclusions Currently, only a small minority of patients initiated on intramuscular vitamin B12 supplementation derive any meaningful clinical benefit. Furthermore, current testing recommendations for vitamin B12 deficiency are usually not followed.
The authors make several suggestions to improve diagnostic accuracy:
Reserve B12 testing for patients with a clear clinical indication.
Avoid reliance on a single test.
Laboratories should perform reflex testing of MMA levels and IF antibodies when low B12 levels are detected.
Hematologic responses should be followed during treatment and if the expected response does not occur evaluation for other conditions should be carried out.