Determination of erythrocyte vitamin B12 activity

Data presented in this paper show that there is no significant difference between plasma and serum vitam B12 activity when EDTA is used as the anticoagulant. By drawing 5 ml of blood into a tube containing EDTA, the whole blood and plasma B12 activity can be measured using Lactobacillus leichmannii for the assay as the test organism. Erythrocyte B12 levels can be obtained by difference after correcting for hematocrit. Sodium heparin appears to inhibit the growth of L. leichmannii.