Knowledge Check

Regarding the complete blood count in vitamin B12 deficiency, which of the following is/are true?

Macrocytosis may precede the appearance of anemia

Anemia may be normocytic

Macrocytosis reported to be absent in about 30% of patients.

Which of the following are characteristic findings on the peripheral smear of a patient with vitamin B12 deficiency?

Spur cells

Spur cells are characteristic of cirrhosis.

Macroovalocytes

Polychromatophilia

The number of polychromatophilic cells is reduced.

Hypersegmented neutrophils

Defined as > 5% of neutrophils with ≥ 5 lobes or 1% with 6 lobes. The presence of neutrophil hypersegmentation may be a sensitive marker for vitamin B12 deficiency and may be seen even in the absence of anemia or macrocytosis.

Tear drop cells

True or false: in addition to anemia, vitamin B12 deficiency may cause leukopenia and/or thrombocytopenia.

True

False

The reticulocyte count in patients with vitamin B12 deficiency and anemia is typically:

Low

Normal

High

Vitamin B12 is a cofactor in methylmalonic acid (MMA) and homocysteine Hcy) metabolism, so deficiency of vitamin B12 may lead to increased serum/plasma MMA and total Hcy. Which test is more useful as a marker of vitamin B12 deficiency?

MMA

The specificity of MMA is superior to that of Hcy.

Hcy

Hcy is sensitive but poorly specific for vitamin B12 deficiency.

Which of the following is increased not only in vitamin B12 deficiency but also in folate deficiency?

Methylmalonic acid (MMA)

Elevated MMA may occur in patients with renal insufficiency, small bowel bacterial overgrowth, and hemoconcentration.

Homocysteine (Hcy)

Elevated homocysteine may also occur in patients with folate deficiency, vitamin B6 deficiency, renal insufficiency, hypothyroidism, and with certain genetic polymorphisms.

Which of the following are typically increased in patients with vitamin B12 deficiency?

ALT

Increased AST levels, not ALT.

Indirect bilirubin

LDH

Haptoglobin

Decreased, not increased

Troponin

What causes elevated serum LDH and indirect bilirubin in vitamin B12 deficiency?

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Ineffective erythropoiesis (with lysis of erythroid precursor cells in the bone marrow)

What are two antibodies that may be tested for in pernicious anemia?

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Anti-intrinsic factor antibodies
Anti-parietal cell antibodies

Which antibody is more specific for diagnosing pernicious anemia?

Anti-intrinsic factor (IF) antibodies

IF antibodies (IFA) considered to be a specific marker for pernicious anemia, with reported low false-positive rate of 1%-2%. IFA reported to be positive in 40%-60% of patients with pernicious anemia which increases up to 80% with increasing duration of disease.

Anti-parietal cell antibodies

Anti-parietal cell antibodies are more sensitive than intrinsic factor antibodies for pernicious anemia (80%-90% are positive), but they are less specific.

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