One study of outpatients in Oklahoma using a serum B12 threshold value of <200 pg/mL found that 6% were deficient. (Barnard, 1998) In Seattle,  Washington, researchers determined that 13% of the outpatient study participants were deficient, using values of B12 ≤300 pg/mL and MMA >271 nanomoles per liter (nmol/L).(Rajan, 2002) When the threshold for B12 was set at 300 pg/mL and two metabolic tests were included, 14.5% of participants were considered deficient in a sample of older outpatients in Denver, Colorado. (Pennypacker, 1992)

One conservative study used a threshold value of 180 pg/mL and found that 5.2% of elderly inpatients and outpatients were diagnosed as vitamin B12 deficient. (Matchar, 1994)