An elderly woman has shown in a blood smear test to have large undeveloped red blood cells. Her diet is rich in both plant and animal foods and her plasma folate levels are high. The best explanation would be:

Question

BlackTom AI · Accepted Answer

Consider the clinical picture: an elderly woman with large undeveloped red blood cells on a blood smear suggests megaloblastic (macrocytic) anemia. The dietary intake includes both plant and animal foods, and plasma folate levels are high, which makes folate deficiency unlikely.
Option 1: 'an enzyme fault in folate metabolism' This would typically present with low or abnormal folate function, but the plasma folate level is high in this case, arguing against a folate metabolism defect as the cause.
Option 2: 'anaemia due to poor iron absorption' Iron-deficiency anemia usually shows microcytosis (smaller than normal red cells), not macrocytosis, and does not explain the markedly enlarged, immature red cells observed; thus this is inconsistent with the smear.
Option 3: 'poor cobalamin (B12) levels due to lack of intrinsic factor production' This aligns with megaloblastic changes and macrocytosis; in the elderly, pernicious anemia or other causes of intrinsic factor deficiency reduce B12 absorption, even with adequate or high folate, and explains the smear findings.
Option 4: 'a cobalamin (B12) deficiency due to poor intake' While B12 deficiency can cause megaloblastic anemia, dietary intake of animal products is often sufficient in many individuals, and the question emphasizes lack of intrinsic factor production rather than intake; moreover, if intake were the sole issue, intrinsic factor deficiency would not be needed to explain the problem. The wording is less precise for this clinical scenario where intrinsic factor deficiency is the classic mechanism, especially in an elderly patient.
Overall, the most coherent explanation given the high folate level and macrocytic smear is B12 deficiency due to impaired intrinsic factor–mediated absorption, i.e., pernicious-type lack of intrinsic factor.

An elderly woman has shown in a blood smear test to have large undeveloped red blood cells. Her diet is rich in both plant and animal foods and her plasma folate levels are high. The best explanation would be:单项选择题

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