Abstract: The present invention relates to a new method named the COBASORB test, which can be used for testing the cause of cobalamin malabsorption in humans. The COBASORB test contains three separate tests (first, second and third test) that can be performed separately, sequentially or in random order and number. The first test uses non-radioactive cobalamin for ingestion, the second test uses non-radioactive cobalamin and recombinant intrinsic factor for ingestion and the third test uses recombinant haptocorrin saturated with cobalamin for ingestion. All three tests involve analysis of changes in the concentration of cobalamin saturated transcobalamin (holo-TC) and cobalamin saturated haptocorrin (holo-HC) in the blood. Also disclosed are kits suitable for use in these methods.