The significance of subnormal serum vitamin B₁₂ concentration in older people: A case control study

OBJECTIVES: To determine the clinical significance of subnormal serum vitamin B₁₂ concentration in older people by comparing the hematological, neurological, and biochemical findings in patients with subnormal serum B₁₂ with a control group with normal B₁₂ levels. DESIGN: Clinical and laboratory assessment of hospital patients selected to represent a wide range of serum B₁₂ levels. SETTING: Patients in the medical wards of two hospitals, one a general hospital and the other a geriatric hospital. PARTICIPANTS: Ninety-four older patients, 43 with subnormal (<150 pmol/L) and 51 with normal serum B₁₂ concentrations. MEASUREMENTS: Mini-Mental State Examination, neurological score, full blood examination, mean neutrophil lobe count; serum B₁₂, holotranscobalamin II, total homocysteine, folate, creatinine and gastrin red cell folate; parietal cell antibodies, intrinsic factor antibodies. RESULTS: Of all the measurements, only mean neutrophil lobe count and mean serum total homocysteine were significantly different in the low serum B₁₂ compared with the control group. There was a significant correlation between serum B₁₂ and homocysteine levels. Eighty-eight percent of patients in the test group compared with 76% in the control group showed at least one of the following; elevated serum total homocysteine, neutrophil hypersegmentation, or elevated MCV. This overlap was much reduced when patients with borderline values for serum B₁₂ (150-250 pmol/L) were included in the low B₁₂ group. Most of the older subjects had little or no B₁₂ on transcobalamin II, irrespective of the serum B₁₂ level. CONCLUSION: Almost 90% of older patients with serum B₁₂ < 150 pmol/L show evidence of tissue vitamin B₁₂ deficiency. Deficiency becomes manifest in older patients at relatively higher concentrations of serum B₁₂ than in younger subjects, possibly because of lower levels of holotranscobalamin II in the older patients.