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문제

The nurse is conducting a comprehensive assessment on a client presenting with fatigue and weakness due to suspected vitamin B12 deficiency. Which assessment finding would be most characteristic of this condition?

해설
Vitamin B12 deficiency causes megaloblastic anemia with large, immature red blood cells due to impaired DNA synthesis. Other options describe different types of anemia not characteristic of B12 deficiency.
같은 주제 다음 문제A nurse is conducting an assessment on a 70-year-old client who reports progressive fatigu…

심화 해설


Pathophysiology and Clinical Rationale


Vitamin B12 (cobalamin) is an essential cofactor for two critical biochemical reactions in the body: the conversion of methylmalonyl-CoA to succinyl-CoA and the synthesis of methionine from homocysteine. The latter reaction, catalyzed by methionine synthase, is intrinsically linked to folate metabolism and is indispensable for the production of thymidylate, a nucleotide required for DNA synthesis. When vitamin B12 is deficient, this process is disrupted, leading to a state of ineffective hematopoiesis characterized by nuclear-cytoplasmic asynchrony. The nucleus of developing erythroid precursors in the bone marrow matures more slowly than the cytoplasm, resulting in the production of abnormally large, oval-shaped erythrocytes with a fragile structure. This classic morphological presentation is termed megaloblastic anemia [1][4].



The hallmark laboratory finding is an elevated mean corpuscular volume (MCV), typically exceeding 100 fL. A peripheral blood smear reveals macro-ovalocytes and hypersegmented neutrophils. The study by Zeng et al. reinforces this mechanism by demonstrating that genetic disruptions affecting cubam receptor expression and ribosome biogenesis can precipitate a vitamin B12-dependent megaloblastic anemia, underscoring the direct link between cobalamin utilization and erythroblast maturation [4]. Therefore, the presence of large, immature red blood cells is the most characteristic and pathognomonic finding in a client presenting with fatigue and weakness secondary to suspected vitamin B12 deficiency.





Analysis of Distractors


  • Option 2 (Iron deficiency anemia): This condition results in microcytic, hypochromic anemia characterized by small (low MCV, typically

임상 시나리오

Clinical Practice Guide: Vitamin B12 Deficiency Assessment

Key Assessment Findings:

  • Hematologic: Fatigue, weakness, and pallor due to megaloblastic anemia. Peripheral smear shows macro-ovalocytes and hypersegmented neutrophils.
  • Neurologic: Paresthesias in hands/feet, decreased proprioception, ataxia, and memory loss due to demyelination of the dorsal columns and cerebral cortex.
  • Gastrointestinal: A smooth, beefy red tongue (glossitis) and possible mild diarrhea or constipation.

Diagnostic Workup:

  • Initial Labs: Complete Blood Count (CBC) will reveal an elevated Mean Corpuscular Volume (MCV > 100 fL) and low hemoglobin/hematocrit.
  • Confirmatory Tests: Serum vitamin B12 level (low), methylmalonic acid (MMA) and homocysteine levels (both elevated in B12 deficiency).
  • Underlying Cause: Anti-intrinsic factor and anti-parietal cell antibodies to diagnose pernicious anemia.

Nursing Interventions:

  • Safety: Implement fall precautions due to gait ataxia and impaired proprioception. Assist with ambulation.
  • Nutrition: Educate on dietary sources (meat, eggs, dairy) and provide oral care for glossitis. A soft, bland diet may be tolerated better.
  • Treatment Adherence: For pernicious anemia or severe malabsorption, teach the patient about the necessity of lifelong intramuscular vitamin B12 injections or high-dose oral supplementation.
  • Monitoring: Monitor for signs of hypokalemia during initial therapy as potassium is utilized in new red blood cell production.

핵심 개념

  • Megaloblastic Anemia — A macrocytic anemia characterized by large, immature, and dysfunctional red blood cells (megaloblasts) due to impaired DNA synthesis, commonly caused by vitamin B12 or folate deficiency.
  • Mean Corpuscular Volume (MCV) — A measure of the average size of red blood cells; an MCV greater than 100 fL indicates macrocytosis, a hallmark of megaloblastic anemia.
  • Nuclear-Cytoplasmic Asynchrony — A morphological feature of megaloblastic anemia where the nucleus of an erythroid precursor matures more slowly than the cytoplasm, leading to a large, immature cell.
  • Hypersegmented Neutrophils — Neutrophils with six or more nuclear lobes, a classic and early peripheral blood smear finding highly suggestive of megaloblastic anemia.
  • Intrinsic Factor — A glycoprotein secreted by gastric parietal cells that binds to vitamin B12 and facilitates its absorption in the terminal ileum; its absence leads to pernicious anemia.
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