Microcytic Anemia: A Brief Overview
Corresponding Author: Tungki Pratama Umar, Department of Medical Profession, Faculty of Medicine, Sriwijaya University, Palembang, Sumatera Selatan, Indonesia, Phone: +6285368708668, e-mail: email@example.com
How to cite this article Umar TP. Microcytic Anemia: A Brief Overview. Ann SBV 2020;9(2):42–47.
Source of support: Nil
Conflict of interest: None
Microcytic anemia is caused by hemoglobin (Hb) deficiency synthesis in erythroid precursors, leading to reduced mean corpuscular volume (MCV) of red blood cells. It is the most common type of anemia, primarily due to iron deficiency, followed by chronic disease, and thalassemia. Diagnosis of the spectrum of microcytic anemia requires an adequate history taking and physical examination to search for specific indicators of each disease with a further investigation as indicated for a definitive diagnosis. The treatment of microcytic anemia varies depending on the cause of the disease. The prognosis of the disease also varies depending on the factors underlying the anemia condition.
Keywords: Anemia, Erythrocyte, Iron deficiency anemia, Thalassemia..
Microcytic anemia is caused by a deficiency of hemoglobin (Hb) formation in erythroid precursors, leading to decreased mean corpuscular volume (MCV) of red blood cells.1 The most common causes of microcytosis include iron deficiency anemia and thalassemia. Other less frequent diagnoses that must be considered are including anemia of chronic disease/anemia of inflammation and sideroblastic anemia.2
Microcytic hypochromic anemia seems to be more common throughout premenopausal women since they lose blood during each menstrual cycle, involving up to 30% of women and escalate to 41% in pregnant women.3 This disorder is primarily due to iron deficiency anemia. Iron deficiency anemia is linked with low socioeconomic factors, especially when found in the same family.4,5 Meanwhile, it is estimated that 7% of the world’s inhabitants have thalassemia traits, with 80% of those coming from developing countries.4 On the other hand, anemia of chronic disease is deemed as the second most common source of anemia in the globe, but the detailed statistics on its prevalence are not widely available. This problem is mostly complex and multifactorial, making it difficult to distinguish its components.6 Prevalence involves 33–63% of patients with chronic diseases such as rheumatoid arthritis, chronic kidney disease, or malignancy.7–9 The author would like to give an overview of three commonly found causes of microcytic anemia, including iron deficiency anemia, thalassemia syndrome, and anemia of chronic diseases.
MATERIALS AND METHODS
The review article was searched based on the terms of the Medical Subject Headings (MeSH). The electronic search was performed in three databases, PubMed, Science Direct, and Google Scholar, using four search terms: “Anemia”, “Iron Deficiency Anemia”, “Thalassemia”, and “Anemia of Inflammation”. The criteria for inclusion were: all types of papers related to human studies. The exclusion requirements were: publications with no available full text or not in English. From the papers collected in the first round of searches, additional references have been found through a manual search of the cited references.
Iron Deficiency Anemia
Iron deficiency anemia can occur either absolutely due to exhausted iron stores or functionally when the body’s iron reserves are present or increased, but there is a disruption throughout the supply of iron to the bone marrow.10 These conditions may occur together and develop erythropoiesis and Hb synthesis disorders. This disease is characterized by hypochromic microcytic anemia, decreased serum iron, decreased serum ferritin, elevated total iron-binding capacity (TIBC), declining transferrin saturation, negative bone marrow iron staining, and responsiveness to treatment with iron compounds.11
Iron deficiency anemia can be caused by a lack of iron intake, poor absorption, and iron loss due to long-term bleeding. It is causing an iron-depleted state or negative iron balance. Cases associated with iron deficiency include gastrointestinal, urinary, and female genital bleeding, inadequate quantity or quality (bioavailability) of iron ingestion, increased iron demands, hookworm infestations, and post-gastrectomy patients.4,11 Mechanisms related to iron deficiency anemia are depicted in Figure 1.
Diagnosis of iron deficiency anemia is focused on comprehensive history taking and physical examination. General findings encompass anemic syndrome, which occurs when blood Hb has fallen to %3C;7–8 g/dL. It includes weakness, fatigue, irritability, attention impairment, palpitation, headache, shortness of breath, blurred vision, restless leg syndrome, or tinnitus.12,13 Other findings include pica, particularly in the form of pagophagia (eating ice cubes for %3E;2 months). In addition to dietary status, the history of chronic bleeding, including gastrointestinal or heavy menstrual bleeding, needs to be addressed.4,11 Meanwhile, clinical findings on physical examination comprise of koilonychia, papillary atrophy of the tongue, angular cheilitis, gastric mucosal atrophy, and Plummer–Vincent (Paterson Kelly) syndrome.4,11,14
Laboratory evaluation is one of the mainstays of the diagnosis of iron deficiency anemia. Laboratory diagnosis showing microcytic hypochromic anemia in peripheral blood smear, decreased MCV, mean corpuscular hemoglobin (MCH), iron serum, ferritin, and transferrin saturation, in addition to increased TIBC, and negative iron staining (Prussian Blue) on bone marrow analysis (rarely done) are the most frequent findings.11 A further test for finding the exact etiology of iron deficiency anemia may be performed, including the fecal examination (for hookworm infestation) using a semi-quantitative (Kato-Kaz) method, an occult blood test, barium in-loop, or endoscopy as indicated.11
The concept of treating iron deficiency anemia is a causative treatment to prevent recurrent anemia and the use of iron preparations to correct iron deficiency in the body (replacement therapy).9 Oral iron supplementation is the first preference due to its efficacy, cost-effectiveness, and safety. The most commonly used agent is ferrous sulfate at a dosage of 200 mg three times a day, each containing 66 mg of elemental iron. Its supplementation can increase erythropoiesis up to three times than normal conditions.9 Other regimens include ferrous fumarate, ferrous gluconate, ferrous succinate, and ferrous lactate.9 However, oral iron tablets have a possible detrimental effect on gastrointestinal comfort (up to 15–20% of patients), resulting in reduced adherence. To avoid this disorder, iron supplementation can be given during meals or at a reduced dose.9 Iron supplementation must be done for a minimum of 3 to 6 months and accompanied by vitamin C consumption to increase its absorption, in addition, to consume foods with high iron content.9
If oral iron supplementation is not well tolerated, counterproductive (e.g., ulcerative colitis, post-gastrectomy), or in a situation with a high demand of iron with a limited period of time available (e.g., third trimester of pregnancy or before surgery), parenteral iron supplementation can be considered.15,16 The available regimens include iron dextran, iron sorbitol citric acid, iron sucrose, and ferric gluconate. Some adverse reactions related to parenteral administration include pain, skin hyperpigmentation, anaphylaxis, headache, flushing, phlebitis, nausea, vomiting, abdominal tenderness, and syncope. It is useful to increase the level of Hb and rise iron storage for up to 500 to 1,000 mg.9
Anthelmintic agents can be used for particular causes of iron deficiency anemia (hookworm or Schistosoma infestations). According to the World Health Organization Guideline, hookworm infection can be successfully treated either with albendazole (400 mg single dose; SD), mebendazole (500 mg SD), levamisole (2.5 mg/kg SD), or pyrantel (10 mg/kg SD). In the meantime, when endemic urinary schistosomiasis is present, annual praziquantel (40 mg/kg SD) treatment may be administered.17 A systematic review by Smith and Brooker suggested that anthelmintic treatment is effective for improving the Hb levels of infected populations, but the impact differs depending on the form of benzimidazole drugs and the package of treatment interventions.18
Iron deficiency anemia is a rather easy disease to treat. The effects of oral iron therapy are very impressive. However, this disorder frequently recurs when compounded by comorbids that are difficult to treat, such as malignancy. In pregnant women, this disease was associated with increased mortality, increased preterm delivery, and low birth weight infant.4
Thalassemia syndrome is a heterogeneous group of hereditary anemia characterized by defective synthesis of one or more globin chain subunits of Hb tetramer. The clinical syndrome associated with thalassemia is the outcome of the combined consequences of insufficient Hb development and imbalanced accumulation of globin subunits.19
The pathophysiology of the clinical symptoms of thalassemia is very complex and involves the interlinking of intracellular and extracellular processes. The element that plays the most part in deciding the clinical picture is the unnecessarily high precipitation of single globin chains due to the absence of other partners to construct the Hb molecule.4
The basic mechanism underlying β-thalassemia is the deficiency of β-globin synthesis due to mutation of the HBB gene in chromosome 11.20 This results in an HbA deficit and a surplus of free α-globin chains. Low HbA synthesis results in a decrease in erythrocyte weight and volume (MCH and MCV). The excess of an α-globin chain, which is relatively insoluble in plasma, will stick and accumulate as an inclusion of the bodies in the erythroid precursors, destroying these cells before being differentiated into mature erythrocytes (intra- and extramedullary).21 This is referred to as inefficient erythropoiesis.
Patients with α-thalassemia develop excessive β-globin and γ-globin chain due to defects in the HBA1 and HBA2 genes in chromosome 16.20 In comparison to the α-globin chain, the globin-β and -γ chains are relatively soluble in the W shape of the tetramers, HbH and HbBart. These chains destroy more erythrocytes than an erythroid precursor. This is why α-thalassemia demonstrates more clinically hemolytic anemia than ineffective erythropoiesis.21,22 The abundance of the β-globin chain causes the oxygen dissociation curve to be disrupted.20 The mechanism for thalassemia is illustrated in Figure 2.
Several conditions linked to the disorder could be asked for in the history-taking of thalassemia patients. These include chronic pallor (including onset age), history of recurrent transfusions, family history of thalassemia and recurrent transfusions, an enlarged and full sensation of the stomach (hepatosplenomegaly), ethnic susceptibility (Mediterranean, Middle East, India, and South East Asia), and a history of late development and puberty.23,24
The results of the physical examination of a patient with thalassemia depend on the type of thalassemia and the degree of severity. This is exemplified in α-thalassemia, which is identified as a silent carrier or α-thalassemia—a trait that is only asymptomatic or developing mild symptoms, whereas, in HbH patients, it can have moderate to severe symptoms and is accompanied by clinical findings of hemolytic anemia, jaundice, hepatosplenomegaly, and bone deformities. Another type, the Hb Bart Hydrops Fetalis, is generally lethal to the fetus.4 The same applies to β-thalassemia, where it is usually asymptomatic in minor cases, but when the patient comes with a major type, they require regular transfusions and developing various disorders such as failure to grow, progressive pallor, diarrhea, eating disorders, irritability, recurrent infection (fever), and organomegaly (liver and spleen), with intermediate thalassemia stating the condition between minor and major cases. On the other hand, transfusions that are not properly administered may cause hyperpigmentation of the skin, jaundice, underdeveloped muscle growth, optic neuropathy, chronic hypercoagulation, leg ulcers, and bone deformities such as genu valgum, cranium cortex thinning, and osteoporosis due to extramedullary hematopoiesis.4,25
β-thalassemia—clinical findings linked not only to insufficient transfusion but also to excessive transfusion. This process triggers an iron overload condition that can lead to growth issues, inability to achieve mature sexual function, hepatic cirrhosis, endocrine system disorders (diabetes mellitus, pituitary, thyroid, and adrenal dysfunction), and cardiac problems (cardiomyopathy and arrhythmias).25,26
The gold standard in the diagnosis of thalassemia is Hb electrophoresis using the quantitative Hb variance test method, quantitative HbA2, HbF, capillary Hb electrophoresis, or high-performance liquid chromatography (HPLC).23,25 Hemoglobin electrophoresis is mainly useful for a patient with β-thalassemia, which will show increased HbA2 and HbF (up to 95%). It can also show some Hb variants, including HbH disease, HbC, HbE, and HbS disorder.27 Other laboratory findings include severe anemia (Hb %3C;7 g/dL, particularly in thalassemia major), a reduction in the erythrocyte index, with MCV values <75 fL, MCH <27 pg, and an increase in red cell distribution width (RDW) of about 50%, Mentzer Index <13 and a rise in reticulocytes.23,28 Peripheral blood smear analysis can show the existence of hypochromic microcytosis cell, anisocytosis and poikilocytosis, target cells, Pappenheimer’s body, basophilic stippling, and nucleated erythrocytes with leukopenia, neutropenia, and thrombocytopenia in hypersplenism cases.23 For certain cases (such as in patients who have undergone multiple transfusions or have established uncommon forms of Hb), DNA analysis can be considered.23 This analysis can be performed using a reverse-dot-blotting technique, allele-specific PCR, real-time PCR with melting curve analysis, and DNA sequencing approach that can detect more than 200 mutations in thalassemia-β (mainly HBB gene) and other forms of thalassemia and hemoglobinopathies.27,29–31 The use of this technique can also be extended to chorionic villus sampling for prenatal diagnosis of thalassemia.32
The primary treatment for patients with thalassemia is blood transfusion, followed by iron chelation. The purpose of this action is to suppress extramedullary hematopoiesis as well as to maximize the development of the child. The judgment for blood transfusion is very individual in each patient. But, some criteria that can be applied for supporting transfusion decision are the laboratory test which proves that the patient has thalassemia major, Hb <7 g/dL and has development problems, and/or bone deformities due to thalassemia.23 The transfusion is required to maintain a pre-transfusion Hb level of between 9 and 10.5 g/dL and is recommended to be administered every 2–5 weeks.28,33 Ideally, the blood product used for transfusion does not pose any harm or adverse effects to the patient. These products include washed erythrocyte (WE) and leuko-depleted packed red cells.23,34,35 Patients should be tested for blood and antigen type, kidney function, liver function, and iron status at the start of the transfusion and considered vaccination against hepatitis B and C, as well as parvovirus B19A and B, in addition to monitoring the production of new antibodies to avoid transfusion reactions.23,24,33
Iron-chelating agents are used to avoid long-term complications of transfusion (iron overload) in different organ systems, thus minimizing the mortality of thalassemia patients. Its main action is related to free iron-binding and iron elimination.4,36 The basis for initiation of chelation is usually established when the cumulative transfusion has reached 10–20 units of red cells or serum ferritin %3E;1,000 ng/mL.37,38 Several other parameters that can be taken into account are transferrin saturation, liver iron concentration, or the occurrence of cardiac hemosiderosis in T2* MRI (up to <10 ms in extreme cases).23,39 The available types of iron-chelating agents including deferoxamine (subcutaneous injection), deferiprone, and deferasirox (oral regimen).40 Recent studies indicate the possible advantage of combining iron-chelating agents to improve effectiveness in the preventive measures of cardiac and hepatic siderosis.41
With the advancement of transfusion technologies and the advent of iron chelation, many patients with thalassemia are reportedly able to marry and live properly with a median survival of up to 31 years (compared to 17 years in patients without sufficient treatment).4,21 However, improved life expectancy is associated with multiple comorbidities such as failure to reach spontaneous puberty (50%), heart failure (70%), hypothyroidism (10%), diabetes mellitus (6%), and psychosocial disorders.21
Anemia of Chronic Disease
Anemia of chronic disease or inflammation is the term used to describe hypoproliferative anemia shown in response to chronic infection, chronic immune activation, and malignancy that has occurred for >1 to 2 months.4,6 This is the second most common cause of anemia after iron deficiency.42 Characteristics of this condition include Hb levels 7–11 g/dL, decreased serum iron levels followed by low TIBC levels, high levels of iron tissue deposits, and decreased synthesis of red blood cells.4
Anemia due to chronic disease is complex and multifactorial. This condition is associated with a disruption in the immune system that causes shortened erythrocyte survival, impaired cell proliferation of erythroid progenitors, and increased uptake of iron and cell retention in the reticuloendothelial system.42,43
The basis of the mechanism of anemia in chronic diseases is associated with the involvement of hepcidin (including cytokines), as well as decreased erythropoietin (EPO) and erythroid responses. Increased production of hepcidin in response to chronic infection/inflammation induces iron retention in macrophages and hepatocytes, rendering it inaccessible for erythropoiesis, leading to anemia, even though iron reserves are still high (elevated ferritin).44,45 Hepcidin itself binds to the ferroportin receptor, an iron protein present in macrophages, hepatocytes, enterocytes, and placental syncytiotrophoblasts.46,47 An inflammatory mechanism that raises the release of cytokines such as interleukins (IL-1 and IL6) and tumor necrosis factor-alpha (TNF-α) accompanied by the activation of monocytes and activates a cascade involving interferon secretion (IFN-B and IFN-γ) by T11 lymphocytes plays a role in anemia of chronic disease.6,42 Cytokines may exert direct toxic effects on the progenitor cells by inducing the formation of labile free radicals such as a nitric oxide or superoxide anions by macrophage-like cells.6 This will reduce the response of the bone marrow to EPO and thus restrict the proliferation and differentiation of erythroid progenitors, especially in erythroid colony-forming units and erythroid burst-forming units.6,48,49 Cytokines are also believed to play a role in triggering red blood cell precursor apoptosis, reducing EPO receptors in the progenitor cells, and suppressing EPO expression in the kidney cells.6,42,50
Anemia of chronic disease needs to be examined for the exact underlying disease. It is largely focused on the exclusion of other forms of anemia. Chronic virus infections (human immunodeficiency virus/HIV), fungal, parasite, and bacteria (tuberculosis) must also be evaluated.51 Secondary anemia may also occur in individuals undergoing post-organ transplantation immunosuppressive treatment, an autoimmune disorder (rheumatoid arthritis, systemic lupus erythematosus), or other chronic diseases (e.g., malignancy, chronic kidney disease).52,53 Symptoms that can occur include malaise, weakness, myalgia, palpitations, insomnia, manifestations of orthostatic hypotension (dizziness, headache), syncope, and lack of appetite. Medical examination can reveal pale skin, impaired neurological and cognitive ability, orthostatic hypotension, arrhythmias, tachypnea, and hepatosplenomegaly.4
Laboratory tests can be based on the evaluation of iron parameters, bone marrow studies, and other blood tests.53 Hypoferremia (decreased serum iron concentration) is present due to the reduced transferrin protein synthesis, but there is also an increase in serum ferritin caused by inflammation.54 Bone marrow aspiration or biopsy is rarely done and typically the bone marrow looks fine unless it is directly affected by the underlying illness. The findings that may characterize anemia due to chronic disease entail decreased sideroblasts accompanied by the increased iron content of macrophages.54 Other measures that can be found include microcytosis, increased content of free protoporphyrin, elevated levels of fibrinogen, ceruloplasmin, haptoglobin, C-reactive protein (CRP), orosomucoid, C3, and amyloid A protein, negative nitrogen balance, and decreased serum transferrin receptor concentration (FRT)/log ferritin to <1.4,42 The selection of workup is mainly related to the causes behind the anemia (disease-specific).
The key concept in the treatment of chronic disease anemia is to treat the underlying disease and deficiency replacement.53 The evaluation of the staging and treatment history of comorbidities should also be carried out to estimate the degree of impairment and baseline hematopoietic conditions.51 Administration of blood transfusion is suggested in cases of hemodynamic disturbances, particularly at Hb levels <8 g/dL which is accompanied by bleeding55 and established at 10–11 g/dL.42 Erythropoietin is effective in patients with cancer, kidney failure, multiple myeloma, rheumatoid arthritis, and HIV infection. Current medication categories include EPO alpha, beta, and darbepoetin. Giving these compounds can prevent the side effects of transfusion and have anti-inflammatory effects.4 The Kidney Disease Improving Global Outcome (KDIGO) guideline suggests that EPO be prescribed on an individual basis when Hb falls <10 g/dL and does not surpass 13 g/dL. This goal is related to lower mortality and hospitalization rates.4,56 On the other side, iron supplementation is controversial because of its role as a food source for microorganisms,4 but also its benefit in inhibiting TNF-α secretion. The latest recommendation indicated that iron supplementation can begin in true iron deficiency states.42 Other treatments can contain 1 mg of folic acid per day, which may be increased to 5 mg in patients with serious malabsorption of vitamin B12.4
The prognosis of patients with chronic anemia varies widely. Morbidity and mortality are strongly dependent on the underlying illness, whether at an early or advanced stage.4 However, the correction of the anemia is assumed to enhance the capability of the patient activity to ensure a better quality of life.57
Microcytic anemia is anemia defined by the development of red blood cells in smaller sizes than normal conditions. Microcytic anemia causes include iron deficiency, thalassemia, and chronic disease. The treatment of each form of microcytic anemia varies depending on the underlying cause.
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