Correlation of serum and urine vitamin B12.

The relation between the serum vitamin B(12) level and the daily loss of vitamin B(12) in urine was examined in patients with normal serum vitamin B(12) levels and in patients suffering from vitamin B(12) deficiency. A linear correlation was found between the two measurements, suggesting that the serum vitamin B(12) level is a governing factor in the urinary loss of vitamin B(12). The contribution by this loss to the total loss of vitamin B(12) from the body is small under normal circumstances but becomes quantitatively more important with the depletion of body stores.