Assess folate status using serum and RBC folate measurements. Deficient: serum folate below 2.0 ng/mL, RBC folate below 140 ng/mL. Borderline: serum folate 2.0-3.0 ng/mL. RBC folate better reflects tissue stores. Causes: poor dietary intake, alcohol, malabsorption (celiac), medications (methotrexate, trimethoprim, phenytoin, sulfasalazine), pregnancy (increased demand).
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