in a study from four laboratories using two commercial vitamin b12 radioassays ( impure hog intrinsic factor concentrate containing both intrinsic factor and r binders ( if + r ) to measure total corrinoids and the same concentrate presaturated with cobinamide ( cbi ) to block b12 binding sites on r binder ( if + r + cbi ) to measure only cobalamins ) , the rank order of results was generally the same .
C0304938
intrinsic factor concentrate
C0021918
intrinsic factor