Pediatric Iron Toxicity Workup

Updated: Aug 04, 2020
  • Author: Christopher P Holstege, MD; Chief Editor: Stephen L Thornton, MD  more...
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Laboratory Studies

Iron toxicity is a clinical diagnosis; any studies are simply adjuncts. Toxic effects of iron may occur at doses of 10-20 mg/kg of elemental iron.

Little is known about the absorption rate of iron in an overdose, the timing of peak serum iron levels, or the rate at which serum levels fall from their peak levels. Serum iron levels generally correlate with clinical severity and are as follows:

  • Mild - Less than 300 µg/dL
  • Moderate - 300-500 µg/dL
  • Severe - More than 500 µg/dL

Difficulties involved with interpretation of serum iron levels include the following:

  • The ideal serum iron level is a peak level at 2-6 hours postingestion, and the time from ingestion is often unknown.

  • Deferoxamine interferes with standard assays and leads to falsely decreased iron levels.

  • Serum iron levels may not be available in a timely fashion. Serum levels obtained more than 8-12 hours postingestion may not be useful because iron redistributes into the tissues and the serum level does not reflect the total body burden of iron.

Total iron-binding capacity (TIBC) has traditionally been used to determine toxicity. Previously, a patient with a serum iron level greater than the TIBC was thought to be at risk for developing systemic toxicity. However, determining the TIBC in the presence of large amounts of iron or deferoxamine may yield a falsely elevated number. Hence, a TIBC above the iron level does not indicate sufficient binding capacity, and this test is not useful in determining the likelihood of toxicity. [7]

Because iron levels are not always readily available, the predictive value of other laboratory test results has been explored. Previously, a white blood cell count greater than 15,000/µL and a serum glucose level greater than 150 mg/dL were said to correlate with iron levels greater than 300 µg/dL. However, more recent studies do not support the predictive value of these ancillary tests, and they are not useful in the setting of iron poisoning.


Imaging Studies

Abdominal radiography may offer information on the iron ingestion, both initially and subsequently. Do not delay treatment for radiography. An initial negative radiographic finding may mean that no iron was ingested or that the ingested iron tablets or solution have dissolved. In addition, liquid preparations and chewable vitamins are not visible on radiographs.

A positive radiographic finding is one that shows radiopaque tablets or particles. This indicates that the ingested iron has not been completely absorbed. Obtaining a radiograph before and after GI decontamination may yield information as to the success of therapy. If the radiographic findings remain positive after decontamination, additional decontamination is required. If the radiographic findings were initially positive and are negative after GI decontamination, this indicates that GI decontamination was successful, although iron levels should still be monitored because of iron absorption prior to initiation of therapy.


Other Tests

The deferoxamine challenge test consists of administering a single dose of deferoxamine, which binds available free iron and is excreted in the urine as the ferrioxamine complex (deferoxamine and iron). This complex changes the urine to a reddish (vin rosé) color, indicating the need for chelation. However, the urine does not change color reliably, even when elevated serum iron levels are present.

This test is not reliable and does not eliminate the need for monitoring serum iron levels. Therefore, one should not rely on the deferoxamine challenge test.