Folate in Serum

Low folate usually reflects inadequate intake — diets low in leafy greens and legumes, or losses from prolonged cooking (folate is heat-labile).

Other causes: malabsorption (celiac disease, IBD, bariatric surgery), chronic alcohol use, increased demand (pregnancy, lactation, chronic hemolysis, exfoliative skin disorders), and folate-depleting medications (methotrexate, sulfasalazine, trimethoprim, phenytoin and other anticonvulsants, metformin).

High folate is most often intake-driven — recent folic acid or B-complex supplementation, fortified foods, or a high-folate meal, since serum folate reflects intake over the preceding days.

It can also accompany vitamin B12 deficiency (the "methyl-folate trap"), where folate accumulates as methyl-THF and can mask the underlying B12 deficiency. Reduced kidney clearance can also raise levels.