Ferritin is the protein that stores iron in cells in almost every organism from bacteria to humans - but its exact structure and mechanism do differ. As a blood test, endogenous ferritin level gives an indirect measure of iron stores. Ferritin <25-30 ng/mL is consistent with iron deficiency anemia - levels higher than this are more difficult to interpret - they don't rule it out.
Whether or not consuming plant ferritin (when you buy "ferritin" supplements that is what you're getting - usually a pea plant) is an effective iron supplementation is another question entirely. And as far as I know there is no great evidence that it is non-inferior to typical oral iron products (salts and saccharide compounds). The ideal treatment for iron deficiency anemia is typically IV iron (or blood transfusion if the anemia is profound enough to warrant it - but IV iron replacement is one of those things coming back into fashion finally after many years of being feared for reasons with poor evidence.
Whether or not consuming plant ferritin (when you buy "ferritin" supplements that is what you're getting - usually a pea plant) is an effective iron supplementation is another question entirely. And as far as I know there is no great evidence that it is non-inferior to typical oral iron products (salts and saccharide compounds). The ideal treatment for iron deficiency anemia is typically IV iron (or blood transfusion if the anemia is profound enough to warrant it - but IV iron replacement is one of those things coming back into fashion finally after many years of being feared for reasons with poor evidence.