Ferritin

Free iron ions are toxic to the cells, as they create reactive oxygen species through the Fenton reaction. They are therefore stored in a protein called ferritin. One molecule of ferritin can store up to 4500 iron atoms. Note that the pure protein-only, non-iron-bound protein is called apoferritin. Ferritin is mostly found in the liver.

Ferritin is a positive acute phase protein.

Ferritin in laboratory medicine

Small amounts of ferritin leaks into the circulation, which can be measured in the serum. Measuring ferritin is the best way to evaluate iron status, for example in the evaluation of suspected iron deficiency. Low levels (< 15 µg/L) indicates iron deficiency, while levels between 15 and 30 indicate decreased iron stores but not overt deficiency.

However, as a positive acute phase protein, levels will be increased in case of inflammation or infection, and so can give a false negative result if these are present at the time of measurement. To evaluate iron status during acute phase reaction, one can measure transferrin receptor.

Elevated ferritin levels are usually due to acute phase reaction, but in the absence of that, high levels indicate iron overload, either due to haemochromatosis, excessive blood transfusion, or iron intoxication. Hepatitis can also cause elevated ferritin levels as ferritin is released from damaged hepatocytes. Elderly can have elevated ferritin levels up to 1000 µg/L without any underlying pathology.

Ferritin levels is measured by electrochemiluminescent immunoassay.