Ferritin
The blood test that measures your body's stored iron.
Ferritin reflects iron storage; it drops before red blood cells become obviously abnormal. Low ferritin (under ~30 ng/mL) suggests iron deficiency even when hemoglobin is still normal, and can cause fatigue, hair shedding, and restless legs.
Medically reviewed by Dr. Ikechukwu Ogbu, MD
MD · Board-Certified, Internal Medicine · Last reviewed June 2026