Transfusion iron overload is a major concern in the management of patients with severe anemic syndromes like thalassemia. Because of the close monitoring of iron homeostasis, excess iron from multiple blood transfusions deposits in different organs of the body and causes organ damage. Early iron-chelation therapy can prevent severe life-threatening consequences.
Transfusion iron overload is directly associated with the number of blood transfusions. One unit of transfused blood contains about 200-250 mg of iron. In general, patients who receive more than 10 to 20 units of blood are at a significant risk of iron overload. Patients who become transfusion dependent with thalassemia, myelodysplastic syndrome, sickle cell anemia, aplastic anemia, hemolytic anemia, etc. inevitably develop iron overload.
The incidence of transfusion iron overload varies in different regions of the world, depending on the scope of early screening and preventive measures. Among 925 patients with transfusion-dependent-thalassemia, 36.7% had myocardial iron overload, as documented on cardiac magnetic resonance imaging (MRI) with a myocardial T2* ≤20 milliseconds. Patients in the West and the Far East had a higher iron burden in myocardium compared to the Middle East. In the United States, around 15,000 patients with sickle cell disorder and 4500 patients with myelodysplastic syndromes and other causes of refractory anemias require regular blood transfusions. Internationally, the number reaches about 100,000.
There is no effective physiological mechanism for the removal of excess iron from the human body. When a red blood cell (RBC) becomes senescent, the reticuloendothelial macrophage phagocytizes it. Inside the macrophage, the heme part of the RBC breaks down into iron and protoporphyrin. Free iron releases into the plasma. Two molecules of plasma free iron (Fe3+) then bind to one serum transferrin, the main iron transport protein. Transferrin then transports iron to the storage site by binding the transferrin receptor. In iron overload stats, transferrin saturation causes labile plasma iron (LPI) and non-transferrin bound iron (NTBI) to readily enter multiple organs through L-type calcium channels (LCC), ZIP14, and divalent metal transporter (DMT1).
Excess iron in the cytoplasm produces reactive oxygen species via the Fenton and Haber-Weiss reaction. Increased reactive oxygen species levels cause mitochondrial damage, peroxidation of lipids, cell membrane damage, and disruption of the electron transport chain. Over time this leads to apoptosis of the target organ. Recent studies suggest that reactive oxygen species levels also impair the production of nitric oxide and damage the vessel wall. Eventually, chronic iron overload contributes to damage to multiple organs, e.g., cardiomyopathy, cirrhosis of the liver, endocrinopathy, arthritis, etc.
Regular histological stains can not identify iron deposited in the tissue. So, special stain, e.g., Prussian blue stain is commonly used to detect tissue iron overload. A blue granular appearance with Prussian blue stain suggests iron deposition in the tissue. In the hepatocyte, iron deposition begins in the periportal areas. It then progressively involves centrilobular areas, Kupffer cells, and biliary epithelial cells. Over time, iron deposition leads to fibrosis and micronodular cirrhosis. Similarly, iron deposition and fibrosis are seen in cardiac myocytes, the pancreas, endocrine glands, and skin.
Most of the patients with transfusion iron overload typically suffer from the underlying symptoms of anemia (e,g., fatigue, breathlessness, pale skin). The physical presentation of transfusion iron overload varies according to the extent and duration of iron overload. Patients with transfusion iron overload usually present with liver disease (e.g., cirrhosis, hepatic failure), cardiac disease (e.g., dilated cardiomyopathy, restrictive cardiomyopathy, arrhythmia, myocardial infarction, congestive heart failure), endocrinopathy (e.g., diabetes mellitus, hypogonadism, hypothyroidism, hypopituitarism), skin pigmentation, and arthropathy.
A serum ferritin level is an inexpensive and widely available way of assessing transfusion iron overload. A patient with thalassemia with a ferritin measurement of more than 2500 ng/dL has an 80% greater chance of cardiac-related mortality. However, a clinician should consider other causes of raised serum ferritin levels (e.g., an inflammatory disorder, malignancy, metabolic syndrome, renal failure, liver disease, excessive alcohol intake) when assessing a patient. Most guidelines recommend serial serum ferritin and transferrin saturation level every three months for a more accurate assessment of the body iron level.
MRI is the gold standard for long term monitoring of liver and cardiac iron levels. Cardiac T2* MRI has a better prognostic value to predict cardiac risk. Most guidelines recommend assessing 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 six months. If the LIC is normal, MRI can be done less frequently (every two years).
Liver biopsy is the standard of care when MRI is not available. However, patient compliance and risk of bleeding have limited its use.
Most guidelines also recommend baseline testing for free thyroxine (T4), thyroid-stimulating hormone (TSH), calcium, phosphate, 25-OH vitamin D, fasting blood sugar (FBS), echocardiography, bone mass densitometry, and follow-up once a year.
Management of transfusion iron overload is based on the duration of transfusion dependence and the severity of the underlying disease. The success of therapy significantly depends on patient adherence. Therefore, the treatment regimen should be adjusted to improve patient compliance.
Prophylactic iron chelation therapy should be initiated before clinically significant iron overload occurs. Phlebotomy is not usually done as most of the patients are already anemic. Traditionally after 15 to 20 units of blood transfusions, an iron-chelating agent is initiated. Deferoxamine and deferasirox are commonly used in the United States.
Deferoxamine is the treatment of choice for transfusion iron overload. It is administered as a continuous intravenous or subcutaneous infusion. In the body, it chelates circulating and tissue iron and eliminates it in urine and bile. In contrast, deferasirox is an orally active iron chelator. After absorption, hepatocyte and other tissues take up deferasirox. Deferasirox chelates tissue iron and eliminates it mainly in bile.
Both deferoxamine and deferasirox monotherapy significantly reduce cardiac and hepatic siderosis. An average deferoxamine dose of 51 mg/kg at least five days weekly reduces the LIC level by 6.4 mg/g DW. An average deferasirox dose of 30 mg/kg per day reduces the LIC level by 3.1 to 7.8 mg/g DW. The dose of iron chelating agents is frequently titred based on serum ferritin, liver, and cardiac imaging. The goal is to keep the serum ferritin level less than 1000mcg/L, and the cardiac T2* less than <20 milliseconds, and the LIC less than 3 mg/g DW. In young children, the dose of deferoxamine should not exceed 25 to 30 mg/kg to minimize adverse effects. Pregnant or breast-feeding patients should avoid chelation therapy.
Medical conditions that mimic transfusion iron overload include hemochromatosis, cardiomyopathy, acute inflammatory conditions, malignancy, arthritis, diabetes mellitus, human immunodeficiency virus (HIV) infection, hemophagocytic lymphohistiocytosis (HLH), dysmetabolic hyperferritinemia, etc.
Several novel concepts are under investigation that may help in the effective treatment of iron overload and the overall survival of the patient. A randomized controlled trial on a calcium channel blocker (amlodipine) as an adjuvant iron chelator shows a significant decrease in myocardial iron concentration. Several phase 2 studies have shown improved adherence with a film-coated oral tablet compared to a dispersible tablet. Gene therapy is another promising option to reduce the transfusion requirement by improving endogenous erythropoiesis. Janus kinase (JAK2) inhibitor and hepcidin analog are currently being investigated as a treatment option.
Iron chelating agents are usually well tolerated by most of the patients. Most of the side effects are dose-dependent and can be easily avoided by a dose adjustment. Regular tests should be performed to monitor chelation associated toxicity. Stop the current medication and re-evaluate if any complications arise.
The side effects of deferoxamine include pain and erythema at the intramuscular or subcutaneous infusion site, acute onset vision loss, deafness, delayed puberty, skeletal dysplasia, anaphylaxis, abdominal pain, nausea, vomiting, diarrhea, increase risk of certain infections (Yersinia enterocolitica, mucormycosis).
The most common side effects of deferasirox are rash, gastrointestinal disturbance, fatal gastrointestinal hemorrhage, renal failure, and hepatic impairment.
Staging plays an important role in the long-term follow up of body iron and determining treatment options. The staging system is based on the LIC level on liver biopsy and is classified as mild (< 7 mg/g DW), moderate (7-15 mg/g DW), or severe (>15 mg/g DW).
The prognosis of patients with iron overload depends significantly on early detection and adherence to preventive measures. For example, it takes about 1.5 months to reduce 50% of liver iron concentration, whereas cardiac iron concentration takes about 13 months. Enhancement of quality of life and survival in transfusion iron overload patients has been steadily improved since the introduction of preventive iron chelating therapy (ICT). Still, mortality in transfusion iron overload is three times that of the general population.
Long term complications of transfusion iron overload are cirrhosis of the liver, hepatic failure, cardiomyopathy, conduction defects, heart failure, diabetes mellitus, hypogonadism, hypothyroidism, and arthropathy. Dilated cardiomyopathy is the most common cause of early death.
Serial monitoring of iron stores can prevent iron overload in patients on chronic transfusion therapy. Serum ferritin levels should be monitored every three months, and a serum iron panel should be done once a year. It is recommended to monitor liver and cardiac iron (either by biopsy or MRI) annually and every 3-6 months in patients with heart failure and intensive chelation therapy. Discussion with the patient and family about the advantages and disadvantages of chelation therapy is important to improve compliance of the patient. Also, patients should be advised to avoid iron-rich food (e.g., red meat, beans, spinach) and also avoid excess vitamin C.
Communication between primary clinicians, hematologists, nurses, and other health care staff is essential for early diagnosis and management of transfusion iron overload. Adherence to follow up and iron-chelation therapy have shown an overall improvement in both morbidity and mortality. The psychological effect of long-term transfusion therapy is common, and early evaluation of depression, anxiety, and other disorders is important. Financial implications for long term therapy should also be considered.
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