Sa1111 Serum Vitamin B12 Levels: Does it Reflect Cellular Deficiency of the Vitamin in Low Normal Range?

Abstract

BACKGROUND: It is unclear whether serum vitamin B12 level accurately reflects its deficiency at the cellular level in the low normal range (200-400pg/ml). Serum homocysteine is a cheap, widely available and sensitive test (95.9%) which has been shown to be a reliable marker for cellular deficiency of vitamin B12. AIMS AND OBJECTIVES: To determine whether patients with low normal serum vitamin B12 levels have vitamin B12 deficiency at cellular level, using serum homocysteine as a surrogate marker MATERIALS AND METHOD: Consecutive patients attending Gastroenterology department at a tertiary care hospital in south India, and found to have serum vitamin B12 levels between 200 to 400 pg/ml, during the period from November 2009 to November 2010, were prospectively enrolled after informed consent. Patients were excluded if any of the following was present: age 1.4, serum folic acid 200pg/ml) and high performance liquid chromatography was used for serum homocysteine (normal<13μM). Data was analyzed using SPSS 16.0. The study was approved by the institutional review board. RESULTS: 50 participants (27male, 23female) with serum vitamin B12 level in low normal range(200-400pg/ml) were enrolled. 74% of the participants had hyperhomocysteinemia suggestive of cellular deficiency of vitamin B12. There was no significant correlation between serum levels of homocysteine and vitamin B12 in the study group (spearman correlation coefficient,r = -0.22, p=0.11). Further analysis was done after including 47 consecutive patients with vitamin B12 deficiency (serum vitamin B12 < 200pg/ml) which revealed a strong inverse correlation between serum vitamin B12 and serum homocysteine levels in patients with vitamin B12 deficiency, ie <200 pg/ml (Spearman correlation coefficient, r = -0.44, p<0.01), unlike the patients with low normal serum vitamin B12 levels, ie 200-400 pg/ml (figure 1). This suggests that serum vitamin B12 may not reflect its deficiency at celluar level, in the low normal range CONCLUSIONS: A majority of patients with low normal serum vitamin B12 levels (200-400pg/ml) have hyperhomocysteinemia, suggestive of vitamin B12 deficiency at cellular level. Serum homocysteine is a useful ancillary test to detect intracellular vitamin B12 deficiency in patients with low normal serum vitamin B12 levels and thereby identify a subgroup with potential benefit from vitamin B12 supplementation.