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Accurate assessment of body iron burden is necessary, not only to diagnose iron overload but also to effectively manage therapy. In addition, given the late onset of clinical symptoms after substantial organ damage has already occurred, it is important that an accurate, non-invasive, readily available screening test for iron overload is available.
A variety of tests are available to assess iron burden or its functional effects. The use of two or more tests will usually be required to define the patient's iron burden and distribution in tissues [1].
Liver biopsy allows the direct evaluation of non-heme liver storage iron and the histochemical examination of differential accumulation of iron in hepatocytes and Kupffer cells. The test also provides insight into liver tissue histology and pathology through assessments of inflammation, fibrosis, and cirrhosis. Liver biopsy is currently the reference method in the clinical/academic research community for assessing total body iron.
Studies have demonstrated the prognostic value of measuring liver iron concentration (LIC) in both hereditary and transfusional iron overload. Patients with thalassemia major who had a LIC above 15 mg Fe/g dry weight (dw) had a higher risk of cardiac complications and early death than those whose LIC was below this threshold [2], suggesting the clinical value of a ‘critical LIC’ level. Threshold levels for hepatocellular injury [3] and fibrosis or cirrhosis [4] are above a LIC of approximately 19–22 mg Fe/g dw. The critical LIC threshold may also be used to guide iron chelation therapy.
Critical LIC values >15 mg/g and approximately 22 mg/g dw predict increased risk of cardiac disease and fibrosis/cirrhosis, respectively [2].
Liver biopsy is an invasive and painful procedure, and carries the risk of bleeding and infection, as well as damage to the liver or surrounding organs. Fatal complications have been reported, although these are rare [5, 6]. The safety of liver biopsy is enhanced by ultrasound guidance; a complication rate of 0.5% was reported in one large study [7]. Sampling errors, especially in patients with cirrhotic livers or low weight sample sizes, have been reported [8].
Heterogeneity of iron distribution in the cirrhotic liver (values relate to LIC)
Image provided courtesy of Yves Deugnier and Bruno Turlin, Liver Unit & Department of Pathology, CHU Pontchaillou, Rennes, France.
A cardiac biopsy enables the histologic assessment of heart tissue changes and iron loading in patients with iron overload. However, like the liver, the distribution of stored iron in the heart is not homogeneous so the test may not provide a true estimate of iron content, particularly in the early stages of disease [9]. In addition, the invasive approach can result in serious complications [10], meaning that the use of cardiac biopsy is primarily restricted to the research rather than the clinical setting.
Other methods available for assessing cardiac iron levels include MRI and the determination of cardiac function, for example using echocardiography and multiple-gated acquisition scanning.
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