Serum iron blood tests are not performed routinely. Most often, serum iron levels are tested if your doctor thinks that you might have too much iron in your blood. A high iron level can be due to a genetic condition, extensive blood transfusions, or rarely due to ingestion of an overdose of iron (usually in children).
Previously, serum iron was also commonly requested when iron deficiency was suspected. However, it is now recommended that the amount of stored iron (in the form of ferritin) rather than serum iron is measured to aid diagnosis of iron deficiency anaemia. Ferritin analysis gives a measure of body iron stores and is a better indicator of iron deficiency than measuring the iron in blood. However, serum iron blood tests can help to identify when anaemia is due to a long-term (chronic) illness.