Elevated iron study results are a frequent laboratory finding that can be a clue to a common genetic disorder. Hereditary hemochromatosis is an inherited disorder of iron metabolism that can cause organ damage from the accumulation of excess iron (1, 2). The most common form of hereditary hemochromatosis (“hemochromatosis type 1”) results from mutations in the gene known as HFE. The specific mutations associated with hereditary hemochromatosis are the substitution of a tyrosine for cysteine at amino acid 282 (C282Y) and the substitution of aspartic acid for histidine at amino acid 63 (H63D) (1, 2). Individuals who are homozygous for the C282Y mutation or who have single copies of both the C282Y and H63D mutations (compound heterozygotes) are susceptible to developing iron overload, with 85% to 90% of hemochromatosis cases occurring in C282Y homozygotes and the remainder occurring in compound heterozygotes (1, 3, 4). In contrast, simple C282Y heterozygotes and H63D heterozygotes and homozygotes are not at risk for hereditary hemochromatosis (2, 4, 5). Additional forms of primary iron overload (hemochromatosis types 2-4) caused by mutations in iron-regulatory genes other than HFE are now recognized (1, 2) but genetic testing for these rare conditions is not routinely available.
Multiple conditions can be associated with abnormal iron study results in the absence of an inherited defect in iron metabolism (6). Secondary abnormalities of iron tests are frequently seen in the context of hematologic diseases, in particular hemolytic anemias, anemia secondary to ineffective erythropoiesis, and disorders treated with multiple transfusions, and in several common types of chronic liver disease. Among the latter group, increased iron studies are seen in up to 50% of patients with alcoholic liver disease, nonalcoholic fatty liver disease, or chronic viral hepatitis (4). In this setting, elevations in transferrin saturation or serum ferritin levels do not invariably reflect the presence of excess iron in the liver or other organs. The clinical significance of elevated iron study results and hemosiderosis in liver disease-and whether this condition requires treatment-remains controversial (6). This contrasts with hereditary hemochromatosis and transfusional iron overload, in which there is consensus that heavy iron loading causes organ damage and that removal of excess iron can prevent these complications (7, 8, 9). Thus, correct identification of the cause of iron test abnormalities is required to determine appropriate treatment.
The identification of the HFE mutations in 1996 was a major step toward improving the accuracy of diagnosis of hereditary hemochromatosis (7). In view of the high prevalence of conditions associated with secondary abnormalities of iron metabolism, HFE genotyping is a useful tool to distinguish hereditary hemochromatosis from these secondary abnormalities. The aims of this study were to investigate the approach of physicians to elevated iron study results at an academic medical center, to assess the accuracy of their diagnoses of hereditary hemochromatosis, and to identify factors that contribute to misdiagnosis.
Material & Methods:
The institutional review board of the University of Iowa approved this study. A list of patients seen at the University of Iowa between January 2002 and May 2006 and between January 2009 and May 2012 with the International Classification of Diseases (ICD) 9th Revision code 275 “disorders of iron metabolism” as a primary or secondary diagnosis was obtained. Patients seen between 2006 and 2009 were not included because transition to a new electronic medical record occurred during this period. A systematic review of the electronic medical records was then performed. Patients with iron deficiency were excluded.
Subjects with no mention of iron overload and no findings in their records suggesting abnormal iron metabolism were considered to be miscoded and were likewise excluded from the study. For patients included in the study, the following data were collected: age at diagnosis, gender, family history of hereditary hemochromatosis, HFE genotype, history of multiple transfusions or known hematologic disease, or evidence of chronic liver disease. Diagnoses of cirrhosis or hepatocellular carcinoma based on clinical findings or imaging or pathology results, and recommendations for or records of phlebotomies were tabulated. The specialty of the diagnosing provider, the year of diagnosis, and the laboratory studies corresponding to that visit were recorded. Laboratory studies included iron levels, total iron-binding capacity, transferrin saturation, ferritin level, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, gamma-glutamyl transpeptidase, and total bilirubin.
The 2011 practice guidelines of the American Association for the Study of Liver Disease were used to assess the appropriate diagnostic strategy and management of hereditary hemochromatosis.4 Transferrin saturation level >45% and ferritin level >250 ng/mL in women and >300 ng/mL in men were considered elevated. Aspartate aminotransferase and alanine aminotransferase >1.5 times the upper limit of normal, which corresponds to 50 U/L in our facility, were considered elevated.
An analysis was done to compare the characteristics of those diagnosed between 2002 and 2006 with those diagnosed between 2009 and 2012. Because the continuous data were not normally distributed, we presented them as medians and interquartile range and used the Wilcoxon rank-sum test to detect statistical significance. For categoric variables, the chi-square test was used. Statistical significance was set at P 45% or increased ferritin (4). One third of patients meeting these criteria in our study did not have a documented HFE genotype. Several factors may contribute to the failure to obtain genetic testing. One is the presence of an obvious cause of secondary iron test abnormalities, which was present in many of the patients who were not genotyped. Whether a decision to forego genotyping in this situation is justified depends on the clinical context, but this does not account for the lack of HFE genotyping in those patients without an obvious cause of secondary iron test abnormalities. Another possibility might be the misconception that elevated iron parameters are unlikely to be a sign of hemochromatosis in the absence of the classic findings of “bronze diabetes,” which are rarely seen (7). Ultimately, the finding that 35% of the patients without a documented HFE genotype were nonetheless diagnosed with hereditary hemochromatosis reflects a knowledge deficit regarding the diagnostic criteria for this condition. Although genetic testing may have been performed elsewhere in some cases, it is doubtful that this was a frequent occurrence, given that neither that information nor external genotyping results were documented in the chart, despite a decision to initiate treatment. These findings are consistent with a previous report suggesting that primary care physicians use HFE testing less frequently than do subspecialty physicians (10).
HFE genotyping is frequently misinterpreted. In our series, hereditary hemochromatosis was diagnosed incorrectly in more than half of the patients with nonhereditary hemochromatosis genotypes. More than two thirds of these misdiagnoses were made by nonspecialists, indicating confusion in the interpretation of HFE genotyping. Several factors may contribute to this confusion. At our institution, HFE genotyping returns with a fairly lengthy description of the testing methodology and its interpretation. Some providers may fail to read the entire report and interpret the presence of a single mutation as diagnostic of hemochromatosis. Further compounding the potential for misdiagnosis is the fact that even in the heterozygous state, the C282Y and H63D mutations can be associated with modest increases in iron parameters (11). Thus, without specific knowledge that these genotypes are not causes of hereditary hemochromatosis, misdiagnosis of hemochromatosis in these circumstances is an understandable error.
Awareness of common causes of secondary iron test abnormalities, in particular chronic liver disease, is low. Patients with nonhereditary hemochromatosis genotypes who present with abnormal iron study results should be carefully investigated for secondary causes of abnormal iron metabolism (4). Non-HFE hereditary hemochromatosis (hemochromatosis type 2-4) should be on the differential in those patients, although these conditions are rare. Among the patients with nonhereditary hemochromatosis genotypes in whom hemochromatosis was correctly ruled out, approximately 90% had a well-defined cause for abnormal iron study results. On the other hand, we were able to retrospectively identify an explanation for abnormal iron study results in approximately three quarters of the misdiagnosed group. In nearly all of those cases, risk factors for chronic liver disease were present, but chronic liver disease had not been recognized as a potential cause of iron test abnormalities. Of note, hematologic causes of secondary iron overload posed little confusion, and most cases of hemolytic anemia, anemia secondary to ineffective erythropoiesis, and history of multiple transfusions were readily recognized as causes of abnormal iron study results. Chronic liver disease was far more common in this study than were hematologic disorders. It seems that many primary care providers may be unaware of the association of elevated iron study results with chronic liver disease. Further compounding the potential for misdiagnosis, iron studies are commonly obtained in the course of evaluation of elevated aminotransferases. In this setting, elevated iron parameters are frequently assumed to be the cause, rather than the consequence, of the underlying liver disease. However, hereditary hemochromatosis is not commonly associated with increased level of liver enzymes, as demonstrated by a recent study showing that the probability of diagnosing hemochromatosis in patients with hyperferritinemia decreases with increased aspartate aminotransferase and alanine aminotransferase levels (12). Our observation that only 18% of patients with hereditary hemochromatosis alone had abnormal liver enzymes is consistent with these findings.
Consequences of Misdiagnosis
Some 38% of the patients with nonhereditary hemochromatosis genotypes and an unknown proportion of those who were not genotyped were treated inappropriately with phlebotomy. Not only is de-ironing not indicated in the absence of an appropriate hereditary hemochromatosis genotype with evidence of expanded body iron stores (4, 13) but also the aggressive phlebotomy regimens used in the treatment of hemochromatosis are potentially harmful. Phlebotomy is not without risks and, if used inappropriately, can cause iron deficiency anemia and fatigue, in addition to psychologic and financial burdens. Of equal importance, an incorrect diagnosis of hereditary hemochromatosis can be a distraction that prevents identification of the actual cause of abnormal iron study results, thereby delaying appropriate treatment.
The appropriate evaluation and management of abnormal iron study results is an area that requires better understanding and knowledge, especially among nonspecialists. Patients with elevated transferrin saturation or ferritin without an obvious cause should be tested for HFE mutations. The HFE genotypes that can cause hereditary hemochromatosis with manifestations of iron overload are C282Y/C282Y and C282Y/H63D (7). All patients in whom the diagnosis of hereditary hemochromatosis is considered should have an HFE genotype documented before treatment with phlebotomy. We suggest that this information be required by the phlebotomy centers before initiation of treatment. Patients with abnormal iron study results and nonhereditary hemochromatosis genotypes should be investigated for other causes of abnormal iron metabolism with particular attention to chronic liver diseases, which are a frequently unrecognized cause of abnormal iron study results. Specialist consultation should be sought for assistance with diagnosis and management.