Vitamin B12 profile assesses vitamin B12 status at the time of sample collection. We will use the Active-B12 test (holotranscobalamin) as a first marker in these investigations. The Active-B12 test measures the biologically active fraction of vitamin B12 which is utilised by cells. Values above our cut-offs suggest good vitamin B12 status. If the Active-B12 result falls within our “grey area” (indeterminate value) we will additionally quantify methylmalonic acid (MMA). This test will confirm vitamin B12 status. In exceptional circumstances e.g. in view of other results (if requested), issues with sample volumes or highly abnormal results, we may also request standard vitamin B12 or plasma homocysteine. These tests may further support the assessment of vitamin B12 status.