To diagnose vitamin B12 deficiency anaemia, your doctor will ask about your symptoms, examine you and may also ask about your medical history. The doctor may ask you to have a blood test. Testing includes a full blood count(FBC) for information about your haemoglobin levels and how many of each of the different types of blood cells you have. A FBC also gives information about the size of your red cells and the amount of haemoglobin in each one. Vitamin B12 deficiency causes enlarged red blood cells. If you have enlarged red blood cells, the condition is called macrocytic anaemia. The levels of vitamin B12 in your blood can also be measured with a blood test. If you have low levels of vitamin B12, you may need to have a test to look for the antibodies that cause pernicious anaemia.
Attribution: BUPA