Hematology · Megaloblastic Anemia
The facts most likely to be tested
Folate deficiency presents as a macrocytic, megaloblastic anemia characterized by an elevated mean corpuscular volume (MCV) and hypersegmented neutrophils on peripheral blood smear.
The most common cause of folate deficiency is inadequate dietary intake, particularly in patients with alcohol use disorder or those who consume few fresh fruits and vegetables.
Folate deficiency is frequently associated with increased demand states, such as pregnancy, hemolytic anemia, or chronic exfoliative skin conditions.
Unlike Vitamin B12 deficiency, folate deficiency does not cause neurologic symptoms such as paresthesias, ataxia, or loss of proprioception.
Laboratory evaluation reveals low serum folate levels and normal methylmalonic acid (MMA) levels, which distinguishes it from Vitamin B12 deficiency.
Certain medications, most notably methotrexate, trimethoprim, and phenytoin, act as folate antagonists and can precipitate deficiency.
Prophylactic folic acid supplementation is mandatory for all women of childbearing age to prevent neural tube defects in the developing fetus.
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A 48-year-old male with a history of chronic alcohol use disorder presents to the clinic complaining of fatigue and generalized weakness. Physical examination reveals pallor of the conjunctiva and a smooth, beefy-red tongue. Laboratory studies demonstrate a hemoglobin of 9.2 g/dL, an MCV of 112 fL, and a peripheral smear showing hypersegmented neutrophils. Serum methylmalonic acid is normal, while serum folate is significantly decreased.
What is the most likely diagnosis?
Folate deficiency anemia
The patient's presentation of macrocytic anemia with hypersegmented neutrophils and normal MMA levels is classic for folate deficiency, which is commonly exacerbated by chronic alcohol use.
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Etiology / Epidemiology
Common in alcoholics, malnourished, and patients on methotrexate. Results from inadequate intake or increased demand.
Clinical Manifestations
Presents with megaloblastic anemia symptoms; glossitis and cheilosis are classic. Lacks the neurologic deficits seen in B12 deficiency.
Diagnosis
Diagnosis confirmed by serum folate < 3 ng/mL. Peripheral smear shows hypersegmented neutrophils.
Treatment
First-line is oral folic acid. Do not treat with folate alone if B12 deficiency is not ruled out.
Prognosis
Rapid hematologic recovery within 2 months. Failure to respond suggests incorrect diagnosis or malabsorption.
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Epidemiology & Etiology
Primarily affects populations with poor dietary intake, specifically the elderly and alcoholics. Increased metabolic demand occurs in pregnancy and chronic hemolytic anemias. Certain medications like methotrexate and trimethoprim act as folate antagonists.
Pertinent Anatomy
Folate is absorbed primarily in the jejunum. Stores are limited, typically lasting only 3-4 months, explaining the rapid onset of deficiency compared to B12.
Pathophysiology
Folate is essential for DNA synthesis and purine production. Deficiency leads to impaired nuclear maturation while cytoplasmic growth continues, resulting in megaloblastic erythropoiesis. This asynchronous maturation causes ineffective erythropoiesis and intramedullary hemolysis.
Clinical Manifestations
Patients present with fatigue, pallor, and glossitis (smooth, beefy-red tongue). Unlike B12 deficiency, there are no neurologic deficits such as paresthesias or ataxia. Severe deficiency can lead to pancytopenia.
Diagnosis
The peripheral blood smear is the most accessible diagnostic tool, revealing hypersegmented neutrophils (>5 lobes). Serum folate levels < 3 ng/mL are diagnostic. Always check serum B12 to avoid masking subacute combined degeneration.
Treatment
Replacement therapy with oral folic acid (1-5 mg daily) is the standard of care. Folate supplementation can mask B12 deficiency symptoms while allowing neurologic damage to progress. Ensure B12 status is normal before initiating high-dose folate.
Prognosis
Hematologic parameters typically normalize within 8 weeks of therapy. Persistent anemia despite supplementation requires investigation for malabsorption syndromes or non-compliance.
Differential Diagnosis
Vitamin B12 deficiency: presence of neurologic symptoms
Myelodysplastic syndrome: refractory to folate supplementation
Alcoholic liver disease: macrocytosis without hypersegmented neutrophils
Hypothyroidism: macrocytosis without megaloblastic changes
Drug-induced macrocytosis: history of hydroxyurea or zidovudine use