The significance of subnormal serum vitamin B-12 concentration in older people: A case control study

OBJECTIVES: To determine the clinical significance of subnormal serum vitamin B-12 concentration in older people by comparing the hematological, neurological, and biochemical findings in patients with subnormal serum B-12 with a control group with normal B-12 levels. DESIGN: Clinical and laboratory assessment of hospital patients selected to represent a wide range of serum B-12 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 homocysteine were significantly different in the low serum B-12 compared with the control group. There was a significant correlation between serum B-12 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 B-12 (150-250 pmol/L) were included in the low B-12 group. Most of the older subjects had little or no B-12 on transcobalamin II, irrespective of the serum B-12 level. CONCLUSION: Almost 90% of older patients with serum B-12 < 150 pmol/L show evidence of tissue vitamin B-12 deficiency. Deficiency becomes manifest in older patients at relatively higher concentrations of serum B-12 than in younger subjects, possibly because of lower levels of holotranscobalamin II in the older patients.