Iron
IJzer
Iron in urine says virtually nothing about the iron stores; the body hardly excretes iron through the kidneys.
Everything about this testWhat it measures
The analysis measures how much iron is excreted in the urine. The body is sparing with iron: most iron is reused and only a very small amount is lost each day, mainly through shed gut and skin cells and, in women, through menstrual blood. Normally virtually no iron leaves the body through the urine. The result therefore says something about excretion and not about the amount of iron you have in store.
- An unusually high iron excretion in the urine, for example when red blood cells break down in the bloodstream or during treatment with a drug that binds iron
High
A raised value is rare. It may fit breakdown of red blood cells within the bloodstream, in which hemoglobin and iron end up in the urine, or treatment with a drug that binds iron and removes it through the kidneys. Damage to the kidney tubules can also increase excretion. A raised value does not mean you have too much iron in your body.
Low
A low or unmeasurable value is normal and expected. The body hardly excretes iron through the kidneys, so a low result says nothing about iron deficiency. If you want to know whether there is an iron deficiency, you need ferritin in blood, possibly together with hemoglobin and the transferrin saturation.
If your result is abnormal
With a question about iron deficiency or iron overload, the GP measures ferritin and, if needed, hemoglobin and the transferrin saturation in blood. An abnormal urine iron on its own does not lead to any standard further testing.
Reliability
Iron in urine says nothing about the iron stores, because the body hardly excretes iron through the kidneys; the meaning of an abnormal value has been little studied. For iron status, the Dutch GP guideline (NHG) on anemia and the Dutch Society for Clinical Chemistry (NVKC) rely on blood tests: ferritin, hemoglobin, transferrin and the transferrin saturation. A single urine sample varies strongly with how much you drink and with what you ate the day before. That is why the result is usually corrected for the creatinine level, or urine is collected over 24 hours.
Limitations
- The body hardly excretes iron through the kidneys; the measured amounts are close to the lower limit of the measurement.
- Fluid intake determines how concentrated the urine is; without correction for creatinine, results are hard to compare.
- Blood in the urine, for example from menstruation or a bladder infection, can raise the result strongly.
- There are no agreed cut-off values; the laboratory decides itself which limit it uses.
How common is this
Iron deficiency is the most common cause of anemia in the Netherlands, especially in women who menstruate. That deficiency is diagnosed in blood and not in urine. Conditions in which iron appears in the urine are rare.
Who is this useful for
A result only really means something for a specific question, such as breakdown of red blood cells in the bloodstream. In people without symptoms, iron in urine adds nothing to the picture of iron status. If you suspect you have an iron deficiency or, on the contrary, iron overload, you need ferritin and the transferrin saturation in blood.
Downsides and risks
- A low result can wrongly be read as iron deficiency, or a high result as iron overload; both require blood tests.
- An abnormal result without agreed cut-off values to interpret it easily leads to unnecessary further testing.
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