Iron
Ferritine
The storage protein for iron; the best single measure of iron stores, but also raised with inflammation.
Everything about this testWhat it measures
Ferritin is the protein in which the body stores iron, mainly in the liver and bone marrow. A small amount ends up in the blood, and that amount keeps pace with the total iron stores: a low ferritin means empty stores, even if the hemoglobin (Hb) is still normal. Ferritin is also an acute-phase protein: with inflammation, infection or liver damage it rises, regardless of the iron stores. That is why it is often assessed together with CRP, the blood count and the transferrin saturation.
- Iron deficiency, even before there is anemia
- Anemia due to iron deficiency (iron deficiency anemia)
- Iron overload, including hereditary hemochromatosis (together with the transferrin saturation)
- A sign of inflammation, liver disease or the metabolic syndrome with a raised value without iron overload
High
A raised ferritin by no means always means too much iron. Because ferritin is an acute-phase protein, it rises with any inflammation or infection, with liver disease, with excessive alcohol use and with the metabolic syndrome (overweight with high blood pressure, high cholesterol or high blood sugar); these are the most common causes of a raised ferritin. True iron overload is more likely if the transferrin saturation is also raised (above 45 percent); that combination may point to hereditary hemochromatosis, a condition in which the body absorbs too much iron from food. Symptoms of iron overload only appear late: tiredness, joint pain (especially in the hand), abdominal pain, a darker skin and, in men, erection problems. Strongly raised values always call for further testing into the cause.
Low
A low ferritin almost always means iron deficiency; there is no other cause that makes ferritin low. According to the Dutch GP guideline (NHG) on anemia, a ferritin below 15 µg/L is proof of iron deficiency, iron deficiency is still quite possible between 15 and 100 µg/L, especially with inflammation, and above 100 µg/L it is virtually ruled out. The most common causes are blood loss (heavy periods, blood loss from the stomach or bowel), an increased need (pregnancy, growth) and a low intake or poor absorption (vegetarian or vegan diet, celiac disease, stomach surgery). Symptoms that go with a deficiency are tiredness, shortness of breath on exertion, hair loss, restless legs and, with anemia, paleness and palpitations.
If your result is abnormal
With a low ferritin, the GP looks for the cause of the iron deficiency: in women with heavy periods it is usually clear, while in men and in women after menopause the NHG guideline calls for examination of the stomach and bowel to rule out blood loss. With a raised ferritin, the GP measures CRP, liver values and the transferrin saturation; if the saturation is above 45 percent and the ferritin stays raised, DNA testing for hemochromatosis (HFE genotyping) follows and, if needed, a referral to the internist (specialist in internal medicine) or gastroenterologist.
Reliability
For iron deficiency, ferritin is the best single blood test: a low value is virtually conclusive, and according to the Dutch GP guideline (NHG) on anemia, a value above 100 µg/L all but rules out iron deficiency. The gray area between 15 and 100 µg/L and any raised value are less clear-cut, because inflammation and liver damage raise ferritin. That is why ferritin is assessed together with CRP and the blood count (Hb, MCV), and with a raised value together with the transferrin saturation.
Limitations
- Any inflammation or infection, even a cold, temporarily raises ferritin and can mask iron deficiency; with a raised CRP the value is harder to interpret.
- Liver disease, alcohol use, overweight and the metabolic syndrome raise ferritin without iron overload.
- Iron tablets and iron infusions raise the value; shortly after an infusion, ferritin cannot be interpreted for weeks to months.
- Reference values differ per laboratory and per sex; the lower limit on the result may differ from the limits that the NHG guideline on anemia uses for iron deficiency.
How common is this
In general practice, anemia newly occurs in about 9 in 1000 people per year; in half of them iron deficiency is the cause, about four times as often in women as in men, especially between 15 and 50 years of age due to menstrual blood loss. Iron deficiency without anemia is even more common. Hereditary hemochromatosis is rarer: about 0.5 to 1.5 percent of the Northern European population carries the predisposition (two copies of the C282Y variant), but only a small proportion of them develop symptoms.
Who is this useful for
Useful with symptoms that fit iron deficiency (tiredness, shortness of breath on exertion, hair loss, restless legs), in women with heavy periods, when planning a pregnancy, with a vegetarian or vegan diet, in endurance athletes and with anemia with small red blood cells (low MCV). Also useful when iron overload is suspected, for example with hemochromatosis in the family, and then always together with the transferrin saturation. In men and in women after menopause with iron deficiency, the GP looks for blood loss from the stomach or bowel; the test does not replace that examination.
Downsides and risks
- A ferritin raised by inflammation or overweight is easily mistaken for iron overload; this can lead to unnecessary worry and testing.
- With confirmed hereditary hemochromatosis, the result also matters for parents, brothers, sisters and children (an incidental finding with consequences for blood relatives).
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results