Normal ferritin levels increase as children grow older, but for teenagers and young girls, the normal range is 7 to 140 nanograms per milliliter, according to WebMD. For adult women, the range is 18 to 160 nanograms per milliliter. Values below these ranges are considered low ferritin levels.
A normal ferritin level varies between different testing labs, according to WebMD. Any lab report confirms the range it is using. A doctor also assesses the results of this test against other measures of health to check if there is a problem. If a low ferritin level is present, it indicates potential iron deficiency, which has a number of causes.