The Vitamin B12 Test is a serological test used to measure the levels of vitamin B12 in your blood. Your body needs Vitamin B12 to make blood cells and ensure the proper functioning of the brain and nervous system. Vitamin B12 deficiency results in the reduction of red blood cells, which is known as pernicious anaemia or megaloblastic anaemia. The Vitamin B12 Test is prescribed as a diagnostic test for macrocytic anaemia and megaloblastic anaemia or pernicious anaemia. For people whose regular reports show signs of these types of anaemias, the Vitamin B12 Test helps confirm the diagnosis. The Vitamin B12 Test is done by taking your blood sample. You can get this test done along with your regular tests or as a single blood test.