Laboratory Assessment

Serum iron levels have been used to determine toxicity and to direct management, but this use is limited, since excess iron is toxic intracellularly and not in the blood. In general, serum iron levels between 300 and 500 pg/dL correlate with significant GI toxicity, and mild systemic toxicity and serum iron levels between 500 and 1000 pg/dL correlate with moderate systemic toxicity. Levels greater than 1000 pg/dL are associated with significant morbidity. Although high serum iron levels support the potential for toxicity, low levels do not connote its absence. Other potential pitfalls in utilizing serum iron levels to predict toxicity include variable times to peak level following ingestion of different iron preparations56 and artifactually lower measured iron levels in the presence of deferoxamine.

Leukocytosis and hyperglycemia have also been examined for their ability to predict iron toxicity. One early study found that a white blood cell count (WBC) of greater than 15,000/pL with glucose level of greater than 150 mg/dL correlated with an iron level of more than 300 pg/dL. 7 This study, however, assumed that a serum iron level of greater than 300 pg/dL denoted toxicity, which is not true in all cases. Subsequent studies were unable to validate the association between these laboratory values and also did not correlate these laboratory values with clinical illness. 89

It was previously accepted that toxicity was not likely when the serum iron level did not exceed the TIBC. Although conceptually valid, TIBC has little value in the assessment of iron-poisoned patients, because it becomes falsely elevated in the presence of elevated serum iron levels or deferoxamine. 10 Additionally, in conditions of chronic iron overload (e.g., thalassemia and hemochromatosis), significant organ pathology occurs despite the TIBC remaining higher than serum iron level.

Use of radiographic studies can lead to diagnostic problems, as well. Radiopaque iron tablets are visible on x-ray and can guide GI decontamination when visualized. However, many iron preparations are not routinely detected, including pediatric chewable and liquid preparations, and negative radiographs do not exclude iron ingestion.9

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