Introduction:
Total vitamin B12 assays (B12) normally show a drop in B12 during pregnancy. Various factors that may be responsible for this include hemodilution, transfer of B12 to the foetus, renal losses secondary to increased glomerular filtration rate, changes in B12-binding proteins and true B12 deficiency. This often makes it difficult to differentiate between a low B12 level and true B12 deficiency. B12 is required for neurological development and deficiency has been linked with neural tube defects, early delivery and intra uterine growth retardation. B12 exists in 2 forms - attached to transcobalamin II (holotranscobalamin) and haptocorrin . Holotranscobalamin is the only way B12 can enter cells. Holotranscobalamin levels have been studied in pregnancy in all three trimesters. The levels tend to fall early and then plateau with a possible increase in the late third trimester. Holotranscobalamin levels are thought to be a more sensitive marker of B12 deficiency.
Objectives
To explore the relationship between total B12 levels and Holotranscobalamin, and determine whether there is a linear relationship between total B12 and Holotranscobalamin.
Methods.
Deidentified retrospective data for 112 pregnant women at Mercy Hospital for Women who had both B12 and Holotranscobalamin assays was analysed between June 2014 to June 2017. Linear regression analysis was used to determine the relationship between these levels. Indications for analysis were not recorded. Our laboratory has a policy that holotranscobalamin levels will only be performed if the total B12 level is less than 200. Normal values B12 156- 658 pmol/L and holotranscobalamin 23- 100 pmpl/L.
Results
There was no correlation B12 levels less than 200 and holotranscobalamin level.
Conclusion
There is no correlation low B12 levels and holotranscobalamin levels this raises the question of the utility of total B12 levels in pregnancy.