In order to determine if a megaloblastic anemia is caused by a B12 or folate deficiency, the following tests can be performed.
The first test is to measure the level of vitamin B12 in the patient’s blood. If the level is low, then a B12 deficiency is likely the cause of the megaloblastic anemia. The second test is to measure the level of folate in the patient’s blood. If the level is low, then a folate deficiency is likely the cause of the megaloblastic anemia.
In addition to these tests, a complete blood count (CBC) should be performed to identify any abnormal red blood cell indices. An elevated mean corpuscular volume (MCV) and an elevated mean corpuscular hemoglobin (MCH) are both indications of megaloblastic anemia and can help to identify the likely cause.
Finally, a bone marrow examination should be performed to confirm the diagnosis. In a B12 deficiency, the bone marrow will show megaloblastic changes in the erythroid precursors. In a folate deficiency, the bone marrow will show a hypersegmented neutrophil, which is an indication of megaloblastic changes.
Overall, determining whether a megaloblastic anemia is caused by a B12 or folate deficiency requires a combination of laboratory tests, clinical assessments, and a bone marrow examination.