Radioactive Vitamin B 12 Absorption Studies: Population Distribution of Plasma B 12 Absorption and Serum B 12

Abstract

Summary

Simultaneous vitamin B₁₂ plasma absorption levels and serum vitamin B₁₂ levels were measured in 1169 consecutive unselected patients. Analysis of the population distribution confirmed the findings of Gräsbeck et al. (1) of a log-normal distribution of the serum vitamin B₁₂ levels. To the contrary, a plot of the cumulative frequencies for distribution of the vitamin B₁₂ plasma absorption levels showed a normal gaussian distribution, except for slight skewing at both extremes. This skewing would be anticipated because of the impossibility of negative values. The mean vitamin B₁₂ plasma absorption level was 3 ± 3.6 pg/ml with a standard deviation of 2.08 pg/ml. Correlation between the plasma vitamin B₁₂ absorption level and the serum vitamin B₁₂ level was 0.1328. When plasma vitamin B₁₂ absorption levels were compared with the logarithm of the serum vitamin B₁₂ levels, the correlation was 0.3722. Eighteen patients were found who had plasma absorption and serum vitamin B₁₂ levels below the 5 percentile. Eight had plasma absorption and serum vitamin B₁₂ values below the 2.5 percentile. An additional eight had plasma absorption measurements below the 5 percentile, while having serum vitamin B₁₂ levels above the 95 percentile. Seven had plasma B₁₂ absorption and serum vitamin B₁₂ levels above the 95 percentile. In no patient was a high plasma vitamin B₁₂ absorption and a low serum vitamin B₁₂ level found.