A particular kind of protein called intrinsic factor (IF) is required for the absorption of vitamin B12. This test looks for the existence of immune system-produced antibodies against intrinsic factor. This causes a deficiency in absorption of vitamin B12. Because vitamin B12 is crucial for the production of red blood cells, a deficiency in it can result in pernicious anaemia (RBCs). If you experience symptoms like pallor, weakness, exhaustion, or tingling in your hands and/or feet, you might need this test. Red blood cells (RBCs) that are larger than usual are another indication of pernicious anaemia.