RBC folate measures folate stored inside red blood cells, reflecting folate status over the preceding 3-4 months. It is far more reliable than serum folate, which fluctuates with recent meals and can appear normal even when long-term stores are depleted.

Folate is essential for DNA synthesis and the methylation cycle. Deficiency causes megaloblastic anaemia, elevated homocysteine, and neural tube defects in early pregnancy. RBC folate is the preferred test for assessing true body folate stores.