Efficacy of hepatic computed tomography to detect iron overload in chronic hemodialysis

Abstract

The diagnostic efficacy of hepatic computed tomography density (HCTD) in comparison with serum ferritin for the detection of iron overload was investigated in uremic patients on maintenance hemodialysis (HD) and in patients with idiopathic hemochromatosis (IHC). Ten IHC patients, 38 HD patients and 40 healthy subjects underwent the CT scanning of the liver and determination of percent saturation of transferrin, serum ferritin concentration and HLA typing. Liver iron content was determined by histochemical grading and direct measurement of liver iron concentration either in IHC patients or in HD patients. Nineteen HD patients were considered to have iron overload on the basis of liver iron concentration exceeding 3.6 μmol/100 mg dry weight. The mean ± SD values of HCTD in healthy subjects, IHC patients, HD patients with iron overload and without iron overload were 60.2 ± 5.6, 79 ± 5.6, 71.4 ± 3.6, 58 ± 3.8 Hounsfield units, respectively. HCTD showed positive correlations with liver iron concentration and serum ferritin either in IHC patients or in HD patients. The analysis of the diagnostic efficacy of HCTD in comparison with serum ferritin for the detection of excessive hepatic iron in HD patients demonstrated that HCTD had higher sensitivity, specificity, positive and negative predictive values. Cut-off points were arbitrarily fixed to 66 Hounsfield units for HCTD, 400 μg/liter for serum ferritin and 3.6 μmol/100 mg dry weight for liver iron concentration. Seventeen HD patients who possessed the histocompatibility antigens associated with IHC, namely HLA-A3 and/or HLA-B7 and/or HLA-B14, had liver iron concentration, serum ferritin and HCTD values higher than those of the HD patients without these "hemochromatosis alleles". The diagnostic approach to the disorders of excessive iron storage of the liver may evolve to a new level of sophistication with the introduction of the CT scanning. HCTD may be an accurate, non-invasive, alternative to liver biopsy for the detection of hepatic iron overload in HD patients and in IHC patients. In HD patients HCTD is more efficient than serum ferritin in diagnosing iron overload. However, liver biopsy, which permits a definition of the presence of fibrosis and cirrhosis, maintains its importance from a standpoint of prognosis and follow-up. In HD patients the presence of any of the histocompatibility antigens of IHC is associated with an increased risk of iron overload and excessive hepatic iron storage.