Free serum vitamin B12 level in certain hematologic disorders.

IN NORMAL HUMAN SERUM, vitamin B12 exists mainly as a heat-labile complex bound to alpha-i globulin. A small fraction is present free or uncombined. Total vitamin B12 content of serum represents the sum of free and bound forms. These fractions are estimable with microbiologic methods. \licrobiologic assay of vitamin B12 in serum is now recognized to be one of the standard methods for proper appraisal of macrocytic anemias. In clinical investigations (lealing with vitamin B12 assay, most of the results have been expressed in terms of either total or combined vitamin B12. The value of free vitamin B12 has, for all practical purposes, been regarded as negligible, and no signfficance has so far been attached to the changes in this fraction. Serum vitamin B12 level has been shown to be grossly abnormal in leuke-mias,1m infectious hepatitis4 and hepatic necrosis.3 The differential pattern of serum \Ijta11 in B11 as obtained in the above conditions refers to either com-l)ined or total vitamin B1.. In the present communication an attempt has been made to study the variation of the free fraction of vitamin B12 in certain hematologic disorders. The data on serum vitamin B12 levels were also analyzed in relation to the in vitro vitamin B12-binding capacity of serum. MATERIALS AND METHoDs Seruimi vitamin B1., Was estimated in 224 subjects: norumal 51, tropical eosinophilia 51, nutritional macrocytic anemia 39, apiastic anemia 33, chronic myeloid leukemia 20, acute nmyeloid leukemia 20 and acute lymphatic leukemia 10. Relevant data for these cases arc shown in table 1. The in vitro vitamin B1,-binding capacity of serum was studied in 51 subjects: nominal 21. nutritional macrocytic anemia 14, aplastic anemia 6, chronic myeloid leukemia 10. 7itanmin B1. assay-Serum samples were collected aseptically from untreated patients for two consecutive days and kept frozen till assay, done usually within three days of collection. Each sample was assayed at least twice. Serumu vitamimin B1. was estimated by the method of Ross6 with the use of Eugleima grad/is var. bacillaris as the test organism. The free or uncombined fraction of serum vitamin B1. was estimated in serum samples heated at 56 C. for 30 minutes. The total vitamin B1. was estimated in serum samples heated at 100 C. for 15 minutes. The difference between time total and free fraction of vitamin B1. represented the bound or combined fraction.