Assessment of vitamin B 12 deficiency and B 12 screening trends for patients on metformin: a retrospective cohort case review

Our study investigated the use of vitamin B testing in a large cohort of patients on metformin and assesses appropriateness and benefits of screening recommendations for vitamin B deficiency. This retrospective cohort study included insured adult patients who had more than 1 year of metformin use between 1 January 2010 and 1 October 2016 and who filled at least two consecutive prescriptions of metformin to establish compliance. The comparison group was not exposed to metformin. Primary outcome was incidence of B deficiency diagnosed in patients on metformin. Secondary outcome was occurrence of B testing in the patient population on metformin. Records dated through 31 December 2018 were analysed. Large hospital system consisting of inpatient and outpatient data base. A diverse, adult, insured population of patients who had more than 1 year of metformin use between 1 January 2010 and 1 October 2016 and who filled at least two consecutive prescriptions of metformin. Of 13 489 patients on metformin, 6051 (44.9%) were tested for vitamin B deficiency, of which 202 (3.3%) tested positive (vs 2.2% of comparisons). Average time to test was 990 days. Average time to test positive for deficiency was 1926 days. Factors associated with testing were linked to sex (female, 47.8%), older age (62.79% in patients over 80 years old), race (48.98% white) and causes of malabsorption (7.11%). Multivariable logistic regression showed older age as the only factor associated with vitamin B deficiency, whereas African-American ethnicity approached significance as a protective factor. Based on our study's findings of vitamin B deficiency in patients on metformin who are greater than 65 years old and have been using it for over 5 years, we recommend that physicians consider screening in these populations.