## Diagnosis: Folate Deficiency Megaloblastic Anemia This patient has folate deficiency secondary to malabsorption from celiac disease. The serum folate is low (2.1 ng/mL, normal >5.4), B12 is normal, and the megaloblastic picture with elevated LDH confirms the diagnosis. ## First-Line Treatment: Folic Acid **Key Point:** Folic acid (pteroylmonoglutamate) is the standard first-line treatment for folate deficiency megaloblastic anemia. Oral dosing is effective when malabsorption is not severe. **High-Yield:** Standard dosing regimen: - **5 mg orally once daily** for 4 weeks, then reassess - Response: reticulocytosis within 3–5 days, Hb rise in 2–3 weeks - Maintenance: dietary supplementation or prophylaxis if ongoing malabsorption ## Why Folic Acid (Not Folinic Acid or Methylfolate)? | Feature | Folic Acid | Folinic Acid (Leucovorin) | Methylfolate | |---------|---|---|---| | **First-line for folate deficiency** | Yes | No | No | | **Mechanism** | Converted to THF by DHFR | Bypasses DHFR (for methotrexate toxicity) | Active form (for MTHFR deficiency) | | **Cost** | Lowest | Higher | Higher | | **Indication** | Nutritional folate deficiency | MTX rescue, not folate deficiency | Genetic MTHFR deficiency | | **Oral bioavailability** | Good | Moderate | Moderate | **Clinical Pearl:** Folinic acid is reserved for rescue of methotrexate toxicity (it bypasses dihydrofolate reductase), not for nutritional folate deficiency. Methylfolate is for genetic MTHFR deficiency, not common folate deficiency. **Mnemonic:** **FAD = Folic Acid for Dietary** — Folic acid is the standard for nutritional/malabsorption-related folate deficiency.
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