# 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?

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> subject: Adult Health

## 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?

## 보기

1. Megaloblastic anemia with large, immature red blood cells **✔ 정답**
2. Iron deficiency anemia with small, pale red blood cells
3. Hemolytic anemia with fragmented red blood cells
4. Aplastic anemia with decreased bone marrow production

**정답: 1**

## 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.

## 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

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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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