Which reflects long-term folate status?

• A. Serum folate
• B. Red blood cell folate
• C. Homocysteine concentration in the blood
• D. Serum methylmalonic acid

Answer: (B)

Long-term folate status is best reflected by red blood cell folate because red blood cells acquire folate during their formation and retain it for the life of the cell, about 120 days. This makes RBC folate a measure of folate stores over weeks to months, not just recent intake. Serum folate, in contrast, can change quickly with meals or short-term dietary changes and doesn’t reliably indicate overall stores. Homocysteine can rise when folate is low, but it’s a functional marker affected by multiple factors (and not specific to long-term folate stores). Serum methylmalonic acid is more specific to vitamin B12 status than to folate. Thus, red blood cell folate best reflects long-term folate status.