A low level of ferritin indicates iron deficiency is present in a body, explains Healthline. A diet low in iron and anemia both cause iron deficiency.
Colon cancer, pregnancy, long-term blood loss due to heavy menstruation, ulcers and hemorrhoids also cause iron deficiency, reports WebMD. In some cases, psoriasis and other diseases cause the loss of iron through the skin and urine, resulting in iron deficiency.
A ferritin test checks for the amount of ferritin in the body, which is a protein that stores and releases iron in the body, explains Healthline. Iron is necessary for carrying oxygen to the cells. For men, average ferritin levels are 24 to 336 nanograms per milliliter of blood, and for women, average ferritin levels are 11 to 307 nanograms per milliliter.