Transfusion Iron Overload

Etiology

Transfusion-related iron overload correlates directly with a patient's number of blood transfusions. Conditions that necessitate repeated transfusions leading to invariable iron overload are:

• β-thalassemia major
• Myelodysplastic syndrome
• Sickle cell disease
• Aplastic anemia
• Hemolytic anemia

One unit of transfused blood contains approximately 200 to 250 mg of iron.[3] Patients who undergo more than 10 to 20 units of blood transfusions face a substantial risk of developing iron overload.[3] No effective physiological mechanism for removing excess iron from the human body exists. For this reason, the body requires tight regulation of iron absorption and recycling. 

Hepcidin, a peptide hormone, regulates iron absorption by binding to ferroprotein, an iron exporter, on the surface of macrophages and enterocytes. Macrophages' daily phagocytosis of red blood cells accounts for approximately 25 mg of iron reclamation. This reclaimed iron is primarily in the ferrous (Fe²⁺) state, which is highly reactive and can cause damage to proteins and DNA. The ferrous iron state prompts ferritin production inside cells, where iron is sequestered and converted into the non-reactive ferric (Fe³⁺) state.

Fe³⁺ binds to transferrin. When the total body iron content surpasses the binding capacity of transferrin, the result is increased levels of the highly reactive ferrous iron in the body, or non-transferrin-bound iron (NTBI). This NTBI is also referred to as labile plasma iron (LPI). Non-transferrin-bound iron enters cells of the heart, liver, pancreas, and endocrine glands that transport other cations like calcium and zinc.[4] The heart, pancreas, and pituitary gland do not accumulate iron, except under pathological conditions.

Hepcidin regulates the release of iron from enterocytes and macrophages into the plasma. Elevated hepcidin levels impede the movement of iron absorbed by enterocytes and stored by macrophages into the bloodstream. Iron overload and inflammation can raise hepcidin levels. Conversely, hypoxia, anemia, and increased erythropoiesis reduce hepcidin, releasing Fe²⁺ into the plasma. Patients with ineffective erythropoiesis, such as those with thalassemia and aplastic anemia, tend to have higher iron levels than their transfusion-dependent counterparts.[5][6]

Epidemiology

In the United States, approximately 15,000 patients with sickle cell disease and 4500 patients with myelodysplastic syndromes and other causes of refractory anemias require regular blood transfusions. Internationally, the number reaches nearly 100,000.[7] The average age of transfusion onset is 4 and 12 for children with thalassemia and sickle cell disease, respectively. The average age for adults is 40 for aplastic anemia and 60 for patients with myelodysplastic syndromes.

The incidence of transfusion iron overload varies in different regions of the world, depending on the scope of early screening and preventive measures. One study reveals that delayed puberty is present in 51% of males and 47% of females with thalassemia. In another study of patients with thalassemia major, one-third were on regular chelation therapy, one-third on intermittent chelation therapy, and one-third on no chelation therapy; 85.64% had iron overload.

Patients in the West and the Far East have a higher iron burden in the myocardium compared to the Middle East.[8] A study in Japan reported that out of 1109 cases of iron overload, 93.1% occurred post-transfusion.[9] In a Greek cohort of transfusion-dependent patients with thalassemia major, 51% had moderate to severe iron overload with serum ferritin of more than 2000 mcg/L and more than 4000 mcg/L, respectively.[10]

Pathophysiology

The clinical manifestations of iron toxicity are silent for many years. The dynamics of iron regulation in the body are multifactorial and become aberrant in transfusion-induced iron overload. Chronic iron overload damages multiple organs, causing cardiomyopathy, liver cirrhosis, endocrinopathy, and arthritis.

The liver is the primary organ that stores iron, and ferritin and hemosiderin are the storage forms of iron. Hemosiderin is an insoluble form of iron storage comprised of trapped ferritin in lysosomal membranes. Hemosiderin does not circulate in blood like ferritin; instead, hemosiderin is deposited in tissues and remains unavailable when cells need iron.[11] When serum transferrin binding capacity is exceeded, LPI levels are high.

Labile plasma iron is highly reactive, toxic, or carcinogenic if present in excess. Labile plasma iron is a highly toxic component due to its high potential to generate oxygen-free radicals, damaging DNA, proteins, and membrane lipids. Ferritin serves as a protective mechanism against LPI. Iron overload occurs when LPI reacts with oxidants, making reactive oxygen species that rapidly degrade the proteins and DNA of a cell.[12] Over time, this leads to apoptosis of the target organ.[13] Recent studies suggest that reactive oxygen species levels also impair nitric oxide production and damage the vessel wall.[14]  

Increased intestinal iron absorption adds to iron overload in some disorders, including beta-thalassemia.[15] In thalassemia intermedia, the exaggerated activity of erythropoietin causes hepcidin deficiency, leading to excess absorption of dietary iron and iron overload. Contrary to this, in thalassemia major, the erythropoietic drive is low, and the iron load is high due to transfusions, leading to higher hepcidin levels. 

Histopathology

Conventional histological stains are incapable of identifying iron deposits within tissues. Therefore, special stains, like Prussian blue, are frequently employed to detect the presence of excess iron in tissues. When stained with Prussian blue, the appearance of a blue, granular pattern indicates iron deposition. In hepatocytes, iron deposition initiates in the periportal areas and progressively extends to involve centrilobular areas, Kupffer cells, and biliary epithelial cells. Over time, this iron deposition results in the development of fibrosis and micronodular cirrhosis. Likewise, we observe iron deposition and fibrosis in cardiac myocytes, the pancreas, endocrine glands, and the skin.[16]

History and Physical

To better assess the patient, clinicians should know how long they have been transfusion dependent, how many transfusions they receive per year, and their compliance with a chelation regimen. Most patients with transfusion iron overload typically suffer from fatigue, breathlessness, and pale skin, which are the underlying symptoms of anemia. The first presenting symptom is often delayed puberty. The remaining complaints vary based on the organ systems affected.[17]

General

• Weight loss
• Fatigue
• Arthralgias
• Pallor
• Breathlessness

Cardiac

Cardiac symptoms are typically due to heart failure.

• Orthopnea
• Dyspnea
• Lower extremity edema
• Paroxysmal nocturnal dyspnea

Endocrine

Symptoms related to the endocrine system are due to iron deposition in the pancreas, thyroid, and pituitary gland.

• Delayed puberty
• Delayed menarche
• Polyuria, polydipsia, polyphagia due to diabetes
• Short stature

Gastrointestinal

Gastrointestinal symptoms are due to cirrhosis.

• Abdominal pain and distension
• Hematemesis
• Melena
• Cognitive deficits, sleep disturbance, bradykinesia, hyperreflexia, rigidity, myoclonus, and asterixis due to encephalopathy 

Physical examination findings vary according to the extent and duration of iron overload. Patients with transfusion iron overload may present with the following:[18]

• Bronze or grey skin color
• Bruising
• Dwarfism
• Cachexia
• Delayed breast development in pubertal girls
• Soft, small testes in males
• Hepatomegaly
• Ascites
• Caput medusa
• Jugular venous distension
• Lower extremity edema
• Pleural effusion

Evaluation

To date, no single lab test exists to mark iron overload. A serum ferritin level is an inexpensive and widely available way of assessing transfusion iron overload. A patient with thalassemia with a ferritin measurement >2500 ng/dL has an 80% greater chance of cardiac-related mortality.[19] However, an inflammatory disorder, malignancy, metabolic syndrome, renal failure, liver disease, and excessive alcohol intake can all lead to elevated ferritin levels making a single result an unreliable indicator of iron overload.[20][21] Most guidelines recommend obtaining serial serum ferritin and transferrin saturation levels every 3 months for a more accurate assessment of the body's iron level.[22] The ferritin level cutoff point for iron toxicity varies in the literature from 1000 ng/mL to 3000 ng/mL. Limitations of ferritin testing are the lack of specificity and interpatient variability. 

Serum iron levels are high in patients with iron overload, and the total iron-binding capacity (TIBC) is low. Serum and total body iron results depend on the method used.[19] Transferrin saturation is easy to measure but far from perfect. A transferrin saturation of over 50% indicates a high iron load. However, this is a dynamic number and could vary with inflammation. 

NTBI and LPI are specific markers for iron overload and may be valuable in monitoring clinical response to chelation therapy. Further studies and standardization of assays are necessary before the routine use of NTBI and LPI levels.

MRI is the gold standard for long-term liver and cardiac iron level monitoring. Cardiac T2* MRI has a better prognostic value in predicting cardiac risk.[23] T2*, measured in milliseconds, is the time required for the organ to lose approximately two-thirds of its signal. A reciprocal relationship exists between T2* and iron concentration as it shortens as iron concentration increases. A T2* <20 ms indicates an increased likelihood of impaired left ventricular ejection fraction (LVEF). Most guidelines recommend a cardiac and liver MRI once a year. If the liver iron concentration (LIC) is more than 0.15 mg/g dry weight (DW) or cardiac dysfunction is present, repeat the MRI every 6 months. If the LIC is normal, repeat the MRI every 2 years. Calculate the LIC using atomic absorption spectrophotometry on tissue obtained from the liver biopsy. MRI of the pancreas is not a good predictor of iron deposition in the pancreas.

The severity classifications of iron overload in the liver are:[24]

• Mild < 7 mg/g dry weight
• Moderate 7 to 15 mg/g dry weight
• Severe >15 mg/g dry weight

A liver biopsy is the standard of care when MRI is not available. However, patient compliance and risk of bleeding have limited its use. Hepatic iron stores are an indicator of total body iron stores. Additional necessary testing is:

• Free thyroxine (T4);
• Thyroid-stimulating hormone (TSH);
• Calcium;
• Phosphate;
• 25-OH vitamin D;
• Fasting blood sugar;
• Hemoglobin A1c;
• Alanine aminotransferase and aspartate aminotransferase;
• Echocardiography; and 
• Bone density testing.[22]

Treatment / Management

Vitamin C enhances iron absorption from food. Patients should avoid vitamin C, alcohol, and iron supplements. Iron chelation therapy is the standard of care to prevent and reverse iron overload. Ideally, prophylactic iron chelation therapy begins before clinically significant iron overload occurs. 

Non-transferrin-bound iron and iron deposited in the liver are the most susceptible to chelation. When to begin chelation therapy depends on when the patient became transfusion dependent and the current damage. The current standard is to begin chelation therapy after 1 to 2 years of consistent or 15 to 20 transfusions. Patients with serum ferritin levels that exceed 1000 to 1500 mcg/L, liver iron levels >3 to 5 mg/g dry weight, or a cardiac T2* of less than 20 ms also warrant chelation therapy. These values correspond to approximately 120 to 200 mL of transfused RBCs/kg. The American Academy of Pediatrics recommends a serum ferritin level < 1500 ng/mL or liver iron < 7 mg/g dry weight for children. The success of therapy significantly depends on patient adherence. Therefore, the treatment regimen should be adjusted to improve patient compliance.

Commonly used chelators in the United States are deferoxamine (DFO), deferiprone, and deferasirox. Before initiating or altering iron chelation therapy, assess patients' iron loading and previous chelation rates.

Deferoxamine, administered as a continuous intravenous or subcutaneous infusion, is the treatment of choice for transfusion iron overload. Deferoxamine helps prevent diabetes, cardiac disease, and cirrhosis. In the body, deferoxamine chelates circulating and tissue iron and eliminates it in urine and bile.

In contrast, deferasirox is an orally active iron chelator that eliminates chelated iron in bile.[25] Once daily dosing and cost make deferasirox more appealing to patients. However, the potential adverse effects of gastrointestinal bleeding, agranulocytosis, neutropenia, thrombocytopenia, hepatic fibrosis, and kidney failure may limit its use. 

Both deferoxamine and deferasirox monotherapy significantly reduce cardiac and hepatic siderosis.[25][26] An average deferoxamine dose of 51 mg/kg at least five days weekly reduces the LIC level by 6.4 mg/g DW.[27] An average deferasirox dose of 30 mg/kg daily reduces the LIC level by 3.1 to 7.8 mg/g DW.[28] The dose of iron-chelating agents is frequently titrated based on serum ferritin, liver, and cardiac imaging. The goal is to keep the serum ferritin level under 1000 mcg/L, the cardiac T2* over 20 ms, and the LIC less than 3 mg/g DW.[29][30][31] In young children, the dose of deferoxamine should not exceed 25 to 30 mg/kg to minimize adverse effects. Pregnant or breastfeeding patients should avoid chelation therapy.[7] (A1)

Maintenance Therapy

Maintenance therapy prevents tissue damage from iron overload.[32] A LIC of more than 15 mg/g dry weight, serum ferritin >2500 μg/L, or cardiac T2* MRI <20 ms indicates inadequate chelation. If there is cardiac iron overload, cardiac iron chelation becomes the primary goal of therapy. Not all patients achieve adequate chelation on one iron chelator. Many patients will need their treatment revised, sometimes needing a higher dose, a different chelator, or a combination of chelators. If transfusional requirements are exceptionally high, more than 200 to 220 mL packed red cells/kg/year, splenectomy can reduce the iron uptake from transfusions. Liver and heart transplantation are considerations for patients who have end-stage disease. (B3)

Differential Diagnosis

Medical conditions that mimic transfusion iron overload are:

• Hemochromatosis;
• Cardiomyopathy;
• Acute inflammatory conditions;
• Malignancy;
• Arthritis;
• Diabetes;
• Hepatitis C;
• Human immunodeficiency virus (HIV) infection; and
• Dysmetabolic hyperferritinemia.[33]

Pertinent Studies and Ongoing Trials

Several novel concepts that may help effectively treat iron overload and the patient's overall survival are under investigation. A randomized controlled trial on amlodipine, a calcium channel blocker as an adjuvant iron chelator, shows a significant decrease in myocardial iron concentration.[34] Several phase 2 studies have shown improved adherence with a film-coated oral tablet of deferasirox compared to a dispersible tablet.[35] Gene therapy is another promising option to reduce the transfusion requirement by improving endogenous erythropoiesis.[36] A janus kinase (JAK2) inhibitor and hepcidin analog are additional investigational therapies.[37][38]

Prognosis

Without chelation therapy, the likelihood of death due to arrhythmia or heart failure is high in late childhood or early adolescence. The prognosis of individuals with iron overload depends heavily on early detection and adherence to preventive measures. Cardiac toxicity and endocrine toxicity are reversible, but the outcomes may vary. Since the introduction of preventive iron chelating therapy (ICT), there has been a consistent improvement in the quality of life and survival of individuals with transfusion iron overload.[39] These individuals continue to face an elevated risk of developing malignancies, and their overall mortality rate is three times higher than that of the general population.[40]

Complications

Without chelation therapy, the likelihood of death due to arrhythmia or heart failure is high in late childhood or early adolescence. The prognosis of individuals with iron overload depends heavily on early detection and adherence to preventive measures. Cardiac toxicity and endocrine toxicity are reversible, but the outcomes may vary. Since the introduction of preventive iron chelating therapy (ICT), there has been a consistent improvement in the quality of life and survival of individuals with transfusion iron overload. These individuals continue to face an elevated risk of developing malignancies, and their overall mortality rate is three times higher than that of the general population.

Complications of Transfusion Iron Overload

Long-term complications of transfusion iron overload are:

• Liver cirrhosis
• hepatic failure
• cardiomyopathy
• cardiac conduction defects
• heart failure
• diabetes
• hypogonadism
• malignancy
• hypoparathyroidism
• adrenal insufficiency and need for stress dose steroids
• hypothyroidism; and
• arthropathy.[40] 

Dilated cardiomyopathy is the most common cause of early death.

Complications of Chelation Therapy

Deferoxamine

• Retinal damage causing night blindness, visual field loss, and retinal pigmentation
• High-tone sensorineural hearing loss
• Growth and bone defects in children causing rickets-like bone lesions, metaphyseal changes, and spinal damage
• Calculate a therapeutic index as the mean daily dose (mg/kg)/current serum ferritin (μg/L). If this is < 0.025 at all times, these side effects of DFO do not occur.

Children should be monitored for visual and auditory deficits every 6 months, and adults every 12 months. Monitor children's growth regularly. Sitting height compared to total height can help signify early spinal growth defects.[41][42][43][44][45]

Deferasirox

• Nausea, vomiting, and diarrhea
• Elevated liver transaminases
• Acute kidney injury
• Auditory and visual changes

Establish baseline renal function. Check renal function monthly or weekly for the first month if the patient has additional renal risk factors. Adjust the dose accordingly based on renal function.[46][47][46] 

 Deferiprone 

• Agranulocytosis
• Elevated liver transaminases
• Arthropathy
• Zinc deficiency

Monitor CBC weekly for the first year and every 2 weeks subsequently. Discontinue therapy if transaminases more than twice normal consistently. Give zinc supplements.