Iron
IJzer
The amount of iron being transported in the blood at this moment; fluctuates strongly and on its own says little about the stores.
Everything about this testWhat it measures
Serum iron is the iron in the blood, bound to the transport protein transferrin, on its way from the gut and the stores to the bone marrow, where it is built into hemoglobin. It is only a small part of all the iron in the body; the stores are in ferritin. The value fluctuates strongly over the day and with meals and therefore says little on its own. Iron is mainly measured to calculate the transferrin saturation (iron divided by the total iron-binding capacity) and is assessed together with ferritin.
- Iron deficiency and iron deficiency anemia, together with ferritin and the transferrin saturation
- Iron overload, including hereditary hemochromatosis, via the transferrin saturation
- Anemia due to a chronic disease (low iron with a normal or raised ferritin)
High
A raised serum iron fits iron overload, but is more often due to something harmless: an iron-rich meal or iron tablets shortly before the blood draw, or the natural morning peak. In hereditary hemochromatosis, iron is raised together with a transferrin saturation above 45 percent and usually a raised ferritin; that combination is the sign, not the iron alone. Liver damage, in which iron is released from liver cells, and some blood diseases with disturbed production of red blood cells also raise the value. Symptoms of iron overload only appear late: tiredness, joint pain, abdominal pain and darker skin.
Low
A low serum iron fits iron deficiency, but also any inflammation or infection and anemia due to a chronic disease: the body then stores iron away and keeps it out of the blood. The distinction is made with ferritin and transferrin: in iron deficiency, ferritin is low and transferrin high; in a chronic disease, ferritin is normal or high and transferrin low. A low iron in the afternoon or evening can also simply be the daily rhythm. Symptoms that go with a deficiency are tiredness, shortness of breath on exertion and hair loss.
Preparation
- Do not take iron tablets or a multivitamin with iron in the 24 hours before the sample is taken. They raise the value temporarily.
If your result is abnormal
The GP never assesses serum iron on its own, but together with ferritin, transferrin and CRP. A raised value with a transferrin saturation above 45 percent and a raised ferritin is repeated, fasting in case of doubt, and if it stays raised, DNA testing for hemochromatosis (HFE genotyping) follows and, if needed, a referral to an internist (specialist in internal medicine) or gastroenterologist. With a low iron and a low ferritin, the cause of the iron deficiency is looked for.
Reliability
Serum iron on its own is an unreliable measure of iron status: the value varies strongly over the day, rises after a meal and falls with any inflammation. The Dutch GP guideline (NHG) on anemia uses ferritin as the first test for iron deficiency and has iron and transferrin measured only to distinguish anemia due to a chronic disease. For iron overload, what counts is not the iron but the transferrin saturation, together with ferritin.
Limitations
- Strong daily rhythm (highest in the morning) and a rise after an iron-rich meal or iron tablets. According to the Dutch medical specialists' guideline (FMS) on hereditary hemochromatosis, a fasting blood draw is not needed; in case of doubt, a raised value is repeated fasting, without iron or vitamin supplements in the 24 hours before.
- Any inflammation or infection lowers serum iron, even without a deficiency.
- A recent iron infusion or blood transfusion makes the value impossible to interpret for weeks.
- Reference values differ by laboratory; some laboratories report only the saturation and not the iron itself.
How common is this
In general practice, anemia newly occurs in about 9 in 1,000 people per year; in half of them iron deficiency is the cause, about four times as often in women as in men. Hereditary hemochromatosis occurs in about 0.5 to 1.5 percent of the Northern European population, but only a small share of the carriers of the predisposition get symptoms.
Who is this useful for
Useful as part of an iron profile (iron, transferrin or TIBC, transferrin saturation and ferritin) when iron deficiency is suspected together with an inflammation or chronic disease, and when iron overload is suspected, for example with hemochromatosis in the family. As a stand-alone test, serum iron has little value: for an ordinary suspicion of iron deficiency, ferritin is the better and sufficient test.
Downsides and risks
- A single raised or low serum iron due to daily rhythm, a meal or inflammation often leads to unnecessary worry; the value can only be interpreted together with ferritin and saturation.
- If hereditary hemochromatosis is confirmed, 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