Ferritin, a major iron storage protein, is essential to iron homeostasis and is involved in a wide range of physiologic and pathologic processes. In clinical medicine, ferritin is predominantly utilized as a serum marker of total body iron stores. In cases of iron deficiency and overload, serum ferritin serves a critical role in both diagnosis and management. Elevated serum and tissue ferritin are linked to coronary artery disease, malignancy, and poor outcomes following stem cell transplantation. Ferritin is directly implicated in less common but potentially devastating human diseases including sideroblastic anemias, neurodegenerative disorders, and hemophagocytic syndrome. Additionally, recent research describes novel functions of ferritin independent of iron storage.

Recent studies have suggested that the presence of iron overload prior to stem cell transplantation is associated with decreased survival. Within these studies, the criteria used to define iron overload have varied considerably. Given the lack of consensus regarding the definition of iron overload in the transplant setting, we sought to methodically examine iron status among transplant patients. We studied 78 consecutive patients at risk for transfusion-related iron overload (diagnoses included AML, ALL, MDS, and aplastic anemia) who received either autologous or allogeneic stem cell transplant. Multiple measures of iron status were collected prior to transplantation and examined for their association with survival. Using this data, three potentially prognostic iron measures were identified and incorporated into a rational and unified scoring system. The resulting Transplant Iron Score assigns a point for each of the following variables: (1) greater than 25 red cell units transfused prior to transplantation; (2) serum ferritin > 1000 ng/ml; and (3) a semiquantitative bone marrow iron stain of 6+. In our cohort, the score (range 0 to 3) was more closely associated with survival than any available single iron parameter. In multivariate analysis, we observed an independent effect of iron overload on transplant survival (p = 0.01) primarily attributable to an increase in early treatment-related deaths (p = 0.02) and lethal infections. In subgroup analysis, the predictive power of the iron score was most pronounced among allogeneic transplant patients, where a high score (≥ 2) was associated with a 50% absolute decrease in survival at one year. In summary, our results lend further credence to the notion that iron overload prior to transplant is detrimental and suggest iron overload may predispose to a higher rate of lethal infections.

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Iron overload at the time of bone marrow transplantation has recently been associated with increased mortality. The mechanism by which iron overload negatively impacts survival is unclear. In an effort to better define iron overload and its potential role in the transplant setting, we examined 78 consecutive patients at risk for transfusion-related iron overload (AML, ALL, MDS, and aplastic anemia) undergoing either autologous or allogeneic stem cell transplant at our institution between 1999 and 2004. To estimate transfusion-related iron overload, we devised a novel scoring system based on routinely available laboratory variables obtained prior to transplant. In our scoring system, a single point was awarded for each of the following: number of red cell units transfused prior to transplantation > 25; serum ferritin > 1000 ng/ml; and a semi-quantitative bone marrow iron stain of 6+. The Transfusion Iron Overload Score (range of 0 to 3) predicted for overall survival in our patient sample (Fig. 1, p = 0.0003 by Kaplan-Meier log rank trend) and was more powerful than using serum ferritin alone (p = 0.02). The calculated score retained its significant association with overall survival while controlling for traditional risk factors (age, sex, diagnosis, transplant type, donor relation, and remission status), inflammation (c-reactive protein), and measures of organ damage (transaminases, total bilirubin, INR, and cardiac ejection fraction) (p = 0.04 by Cox proportional-hazards regression). The 27 patients (35%) with a high score (≥ 2) had a dramatically lower median survival of 5.0 months compared to 29.3 months in those with an iron score of less than two (unadjusted hazard ratio of 2.5; 95% CI of 1.6 to 6.3). The observed mortality seen in those with a high score was primarily attributable to treatment-related mortality (p = 0.018) rather than disease-related mortality (p = 0.48). This finding likely accounts for the significant survival impact of iron overload seen in the allogeneic (p = 0.006) but not the autologous (p = 0.48) subgroup. In conclusion, the Transfusion Iron Overload Score served as a strong independent predictor of survival in our stem cell transplant population, identifying patients at significant risk for early treatment-related mortality. Our results lend further support to the notion that iron overload is detrimental in the transplant setting, and for the first time suggest that transfusion-related iron overload increases mortality via a mechanism independent of pre-existing inflammation and end-organ dysfunction. Figure 1. Overall post-transplant survival by the Transfusion Iron Overload Score. Figure 1. Overall post-transplant survival by the Transfusion Iron Overload Score.