Ferritin test: what your doctor isn't telling you
Ferritin is one of the most useful lab tests for fatigue, and one of the easiest to misread. A result can fall inside the lab's reference range and still be low enough to cause symptoms.
Ferritin measures iron stores — the iron your body has in reserve. It is often the first marker to drop when iron is running low, well before hemoglobin changes. That means someone can have iron deficiency symptoms without meeting the usual definition of anemia.
The problem is the reference range. Many labs list ferritin as “normal” from about 12 to 150 ng/mL for women — a range broad enough to include levels that are technically fine on paper but still associated with symptoms. Ferritin below 30 often gets attention in people dealing with fatigue, hair shedding, brain fog, or poor exercise tolerance. Some clinicians prefer to see it higher when symptoms suggest the low end of the range isn't working well for the patient — roughly 50 to 150, with hair-loss discussions sometimes using 70+ as a working target. A ferritin of 15 getting flagged as fine usually reflects the lab's reference range, not a symptom-based read.
Women of reproductive age are especially likely to deal with low ferritin because of menstrual blood loss and, in many cases, lower iron intake. It also gets missed often. A CBC may stay normal until iron depletion is more advanced, so ferritin never gets checked. In someone with unexplained fatigue, hair loss, restless legs, dizziness, poor focus, or reduced exercise tolerance, ferritin is often one of the first labs worth checking.
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Frequently asked questions
What is a good ferritin level?
A lab may mark ferritin as normal at 12+ ng/mL for women, but a lot of people find symptom relief only at higher levels. Ferritin below 30 is often associated with fatigue, hair shedding, and restless legs. Between 30 and 50 can still be low enough to matter depending on the person. Some clinicians aim for roughly 50 to 150 ng/mL when symptoms suggest the low end isn't cutting it, though targets vary.
Why is my ferritin low even though I take iron supplements?
A few common reasons: poor absorption, ongoing blood loss, gut issues that interfere with absorption, or a form of iron that is hard to tolerate or absorb well. Iron is usually absorbed better away from coffee, tea, and calcium. Some people also do better with ferrous bisglycinate than ferrous sulfate.
Can ferritin be too high?
Yes. Elevated ferritin can point to iron overload, but it can also rise with inflammation, liver disease, or infection. Ferritin is an acute-phase reactant, so a high result does not automatically mean excess iron. When ferritin is elevated, transferrin saturation and an inflammatory marker such as hs-CRP help put it in context.
What tests should I order alongside ferritin?
Ferritin is useful, but it is only one part of the picture. A fuller iron workup often includes serum iron, TIBC, transferrin saturation, CBC with differential, reticulocyte count, vitamin B12, and folate. That makes it easier to tell iron deficiency apart from other causes of anemia and to see whether the problem is storage, absorption, or utilization.