|Year : 2015 | Volume
| Issue : 2 | Page : 95-99
Anemia: An approach to evaluation, 2014
Department of Internal Medicine, Division of Hematology/Oncology, Henry Ford Hospital, Detroit, MI, USA
|Date of Web Publication||16-Mar-2015|
Department of Internal Medicine, Division of Hematology/Oncology, Henry Ford Hospital, 2799 West Grand Boulevard, Detroit, MI 48202
Source of Support: None, Conflict of Interest: None
Anemia is very commonly encountered in general clinical practice among all age groups. The more commonly used way to classify anemia has been to categorize it as being microcytic (mean corpuscular volume [MCV] <80 fL), normocytic (MCV 80-100 fL), or macrocytic (MCV >100 fL), which in turn allows for a more practical way to attempt to come up with a cause for any decrease in hemoglobin. Microcytic anemias are usually due to iron deficiency (in turn, a result of a number of different etiologies ranging from decreased intake, malabsorption, or blood loss), hemoglobinopathies (thalassemic syndromes), and some cases of severe anemia resulting from chronic disease. Normocytic anemia is often a result of anemia of chronic disease, hemolysis, or secondary to bone marrow failure. Macrocytic anemias are frequently caused by deficiencies of folic acid and/or Vitamin B12, exposure to toxic agents like drugs that interfere with DNA metabolism and alcohol, as also bone marrow failure states, such as from myelodysplastic syndrome. A comprehensive history, physical examination, and directed laboratory evaluation will help to identify a specific cause for anemia.
Keywords: Anemia, blood film, evaluation, macrocytic, microcytic
|How to cite this article:|
Kuriakose P. Anemia: An approach to evaluation, 2014. CHRISMED J Health Res 2015;2:95-9
| Introduction|| |
The prevalence of anemia on a global level was estimated at 32.9% in 2010;  the results of the study that led to this percentage estimation only served to highlight the significant role that anemia plays in the overall global burden of disease (GBD). The GBD 2000 report estimated that anemia accounted for 2% of all years lived with disability and 1% of disability-adjusted life-years,  which was echoed in the GBD 2004 update. 
Anemia is very commonly encountered in general clinical practice among all age groups. Although the etiology for such is truly myriad, with a comprehensive history, physical examination, and directed laboratory evaluation, a specific diagnosis can often be arrived at. The more commonly used way to classify anemia has been to categorize it as being microcytic (mean corpuscular volume [MCV] <80 fL), normocytic (MCV 80-100 fL), or macrocytic (MCV >100 fL), which in turn allows for a more practical way to attempt to come up with a cause for any decrease in hemoglobin.  Microcytic anemias are usually due to iron deficiency (in turn, a result of a number of different etiologies ranging from decreased intake, malabsorption, or blood loss), hemoglobinopathies (thalassemic syndromes), and some cases of severe anemia resulting from chronic disease. Normocytic anemia is often a result of anemia of chronic disease (ACD), hemolysis, or secondary to bone marrow failure. Macrocytic anemias are frequently caused by deficiencies of folic acid and/or Vitamin B12, exposure to toxic agents like drugs that interfere with DNA metabolism and alcohol, as also bone marrow failure states, such as from myelodysplastic syndrome.
In an ideal setting, the definition of anemia is a decrease in hemoglobin (or hematocrit) from an individual's baseline value. However, it is not often possible to obtain an individual's baseline hemoglobin level, leading medical personnel to use age, sex, and race-specific reference ranges to arrive at a working diagnosis; commonly, hemoglobin levels tend to be 1-2 g/dL lower in women than in men. Likewise, the value is usually lower amongst Asians and Africans compared to the Caucasian population.
| Microcytic anemia|| |
Since the most common cause for microcytic anemia is iron deficiency, it would make sense to first and foremost rule out its presence, unless, of course, the patient being evaluated comes with a strong history of say a thalassemic syndrome. Measurement of serum ferritin is the definitive test for iron deficiency anemia (IDA), with a low serum ferritin level being commensurate with a state of decreased body iron stores.  Although we are often faced with the dilemma of being uncomfortable in ruling out iron deficiency when the serum ferritin is either normal or high relative to serum iron and transferrin saturation values, it is unlikely that a deficient state might be present in such a scenario. When distinguishing between IDA and ACD, not only is the serum ferritin clearly low in the former, but the total iron binding capacity is classically increased in IDA, and often normal or low in ACD. When the exact status of iron in the body appears equivocal, instead of pursuing a bone marrow biopsy for a more accurate evaluation of IDA,  a therapeutic trial of iron supplementation is a more cost-effective and less invasive way to arrive at this diagnosis. Other parameters that can be used to suspect the existence of iron deficiency include the red blood cell (RBC) red cell distribution width (RDW), which, if increased, favors a diagnosis of IDA over that of ACD. On the other hand, if the RDW is normal, but the MCV is too low for ACD to be suspected, an increase in the RBC count can often point to a thalassemia. Microcytosis without anemia can be seen in thalassemia trait and the iron consumptive state of polycythemia rubra vera.  In the absence of overt inflammation, should the platelet count be increased (reactive thrombocytosis), it can be a pointer toward iron deficiency. While the peripheral blood smear in IDA usually demonstrates anisocytosis and poikilocytosis [Figure 1], with elliptocytes in more advanced states, the presence of polychromasia, basophilic stippling, and target cells is characteristic features in thalassemia.
Having emphasized the role of serum ferritin in helping define the presence of iron deficiency, we can now look at evaluating microcytic anemias that present with a normal serum ferritin. In such a setting, we would need to know whether the microcytosis is new or something that was previously recognized. With preexistent microcytosis, a congenital disorder (thalassemia) should be considered, while if the microcytosis is a recent occurrence, a nonthalassemic condition accompanied by acquired microcytosis should be thought of.
In adults, almost 97% of normal hemoglobin (hemoglobin A) consists of equal quantities of α-globin and β-globin chains (α2 β2). Thalassemia is associated with altered production of either of the 2 normal globin chains (such as α-thalassemia or β-thalassemia), or a structurally abnormal globin chain (such as hemoglobin E). The resulting unbalanced globin chain production leads to microcytosis in the majority of instances, and often manifests in an altered hemoglobin electrophoresis pattern. As such, hemoglobin electrophoresis should be run when the thalassemia is first suspected. Nevertheless, this study does not always detect the presence of thalassemia.
- Alpha Thalassemia: Alpha-globin chain production is controlled by 4 genes (2/haploid chromosome). A mutation of only 1 of the 4 genes causes neither anemia nor microcytosis (silent carrier), while a mutation of 2 of the 4 genes results in microcytosis and often a mild anemia (α-thalassemia trait). When 3 of the 4 genes are mutated, there is excess β-chain production, resulting in the formation of tetramers (hemoglobin H), which manifests as severe microcytic anemia. A mutation of all 4 genes leads to hydrops fetalis, which is incompatible with life. While hemoglobin electrophoresis is normal in the α-thalassemia trait, it is abnormal in hemoglobin H disease. Although genetic testing (polymerase chain reaction-based DNA tests and Southern blot analysis) can reveal the molecular defect in α-thalassemia trait,  family history and ethnicity can help arrive at a working diagnosis, leading to initiation of genetic counseling, without necessarily requiring the former as a starting point
- Beta Thalassemia: Beta-Globin chain production is under the control of 2 genes (1/haploid chromosome), and β-Thalassemia can occur either as a trait (1 of 2 gene mutations) or symptomatic disease (mutation of both genes). Due to decreased production of β-globin chains in β-thalassemia trait, the amount of hemoglobin A2 (α2 δ2) may increase to a little above the normal value (from 2%-3% to 6%). However, a normal hemoglobin A2 level may not entirely exclude the possibility of β-thalassemia trait unless coexistent iron deficiency is ruled out since in the presence of iron deficiency, the expected increase in hemoglobin A2 may not be observed. Hemoglobin electrophoresis in β-thalassemia disease reveals mostly hemoglobin F (α2 γ2), with a slight to moderate increase in hemoglobin F possibly also being seen in β-thalassemia trait and compound heterozygotes. As such, in most instances, genetic testing is unnecessary, and hemoglobin electrophoresis is sufficient for evaluating β-thalassemia
- Structurally abnormal globin chain thalassemia: On account of decreased globin chain synthesis, certain structural hemoglobinopathies can result in a thalassemic (microcytic) phenotype. Three representative examples include:
- Hemoglobin constant spring (resulting from a stop codon mutation and synthesis of a longer, unstable globin chain messenger RNA)
- Hemoglobin E (a structural hemoglobinopathy, prevalent in Southeast Asia, which is a result of an RNA splice site mutation associated with the production of an alternative messenger RNA that is not effectively translated), and
- Hemoglobin Lepore (resulting from the fusion of the δ-and β-globin genes with decreased transcription efficiency). Hemoglobin electrophoresis often helps pick up and distinguish between these thalassemic syndromes, such that genetic testing may not be necessary.
Other microcytic anemias
Anemia of chronic disease and hereditary or acquired sideroblastic anemia are the possible differentials in this setting. Although the anemia in ACD is usually normocytic, a mild amount of microcytosis can sometimes be seen in the setting of the inflammatory anemia. Often, the presence of systemic signs and symptoms help delineate the presence of an underlying disorder which is the cause of the accompanying ACD and helps provide sufficient grounds to arrive at a cause and effect assumption. Sideroblastic anemias are relatively uncommon and are conspicuous by the presence of dimorphic RBCs with increased RDW, along with the presence of ring sideroblasts in the bone marrow.
| Normocytic anemia|| |
The most common reasons for normocytic anemia are either ACD or that related to a primary bone marrow disorder. The former can often be thought of as being the cause when encountered in the right context, such as in the presence of comorbid conditions (diabetes mellitus, connective tissue disease, chronic infections, and malignancy), evidence of inflammatory markers, and an otherwise unremarkable peripheral blood smear. Cytokine-mediated inhibition of RBC production or interference with erythropoietin production and/or function is thought to be at play in this situation. Although ACD is usually normocytic, it can be microcytic, and can at times be mistaken for IDA (low serum iron and transferrin saturation are seen in both). Serum ferritin can help differentiate IDA from ACD [Table 1].  In contrast to ACD, anemia due to primary bone marrow disorder is often accompanied by characteristic changes in the peripheral blood. The presence of pronounced RBC dimorphism, along with oval macrocytes, hyposegmented neutrophils (pseudo-Pelger-Huλt anomaly), or monocytosis can be clues to the presence of myelodysplasia. In myelophthisis, secondary to bone marrow infiltrating processes or metastatic cancer, nucleated RBCs and a left shift in the myeloid lineage is noted. Another example is that of RBC rouleaux formation in multiple myeloma. When making a decision whether or not to obtain a bone marrow biopsy, it is important to consider the likelihood of firstly finding a primary bone marrow disease, and secondly the therapeutic and prognostic value of the information gained. Accordingly, while carrying out such a procedure may be of value in a younger patient with a pertinent history or an abnormal peripheral blood smear, the same may not hold true in an elderly patient with mild anemia, even if the peripheral blood smear was to suggest a primary hematologic disease, since the test result might not affect the overall management decision.
|Table 1: Differentiating between IDA, ACD, and combined IDA/ACD using iron studies|
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Other considerations when encountering normocytic anemia include:
- Iron and Vitamin B12/folate deficiency - These can at times present with a normocytic picture. Therefore, the initial investigation of normocytic anemia should include determination of serum ferritin and serum Vitamin B12/folate levels
- Anemia of renal insufficiency - The severity of the anemia often mirrors the degree of renal insufficiency
- Hemolytic anemia - Laboratory evidence of increased cell destruction (increased lactate dehydrogenase), increased hemoglobin catabolism (increased indirect bilirubin), decreased haptoglobin (a serum protein that binds free hemoglobin), and bone marrow regeneration (reticulocytosis) may be noted. However, these tests are not able to differentiate among the various causes of hemolytic anemia, which are often categorized as being extravascular (in the monocyte-macrophage system of the spleen and liver) or intravascular (lysis within blood vessels) for which the urinary hemosiderin test can be a helpful differentiator [Table 2]. In general, red cell-intrinsic and immune-mediated hemolytic anemias are extravascular while microangiopathic anemias are intravascular.
|Table 2: Differentiating between intravascular and extravascular hemolysis|
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| Macrocytic anemia|| |
It is important to first exclude exposure to alcohol or drugs (common examples being hydroxyurea, methotrexate, zidovudine, 5-fluorouracil). The macrocytosis noted with hydroxyurea is the most pronounced (oval macrocytosis >110 fL), but a lesser degree of macrocytosis (100-110 fL) is seen with the use of zidovudine and chemotherapy (oval macrocytosis in both) or alcohol (round macrocytosis). 
The most important step in patients with macrocytosis is to rule out Vitamin B12 [Figure 2] and/or folate deficiency.  Since recent dietary changes can affect the serum folate level, RBC folate levels are sometimes used to document chronic folate deficiency (RBCs acquire folate at birth, and the cellular concentration does not change during their life span). However, RBC folate assays are not always precise, and instead, the serum homocysteine level may be used to evaluate a deficient state since the serum homocysteine level is increased during folate deficiency due to impaired folate-dependent conversion of homocysteine to methionine. A normal homocysteine level makes the diagnosis of folate deficiency extremely unlikely. In Vitamin B12 deficiency, serum Vitamin B12 levels are usually low. However, the levels may be falsely low during pregnancy, in elderly patients, and in those with low white blood cell counts. In these instances and in patients with borderline-low Vitamin B12 levels in whom the suspicion of a deficient state is being entertained, a more sensitive and highly specific test is the measurement of serum methylmalonic acid level (Vitamin B12 cofactor activity is required to convert methyl malonyl coenzyme A to succinyl coenzyme A). A normal level makes the diagnosis of Vitamin B12 deficiency extremely unlikely.  However, an increased serum methylmalonic acid level is not specific to Vitamin B12 deficiency and can be seen in renal insufficiency or as a result of an inborn metabolic disorder.  Once Vitamin B12 deficiency is confirmed, and a decreased dietary intake is not under consideration, the next step is to screen for intrinsic factor antibodies, which if present, would suggest pernicious anemia. If negative, we would need to think of primary intestinal malabsorptive disorders (such as tropical and celiac sprue, inflammatory bowel disease, amyloidosis, and intestinal lymphoma). 
If vitamin deficiency and drug exposure are ruled out, dividing the MCV value into range cohorts could allow for a degree of etiologic discrimination.
Mild macrocytosis (mean corpuscular volume, 100-110 fL)
The peripheral blood smear can provide additional clues, such as polychromasia (indicative of reticulocytosis) suggesting hemolysis as the cause, whereas round morphology of RBCs, as opposed to oval macrocytosis, might suggest liver disease (with target cells also being seen) or hypothyroidism. 
- Marked macrocytosis (MCV, >110 fL): This is almost always associated with a primary bone marrow disease (such as myelodysplastic syndrome, aplastic anemia, or pure red cell aplasia), for which a bone marrow biopsy is indicated if the specific hematologic diagnosis were to affect management decision.
| Conclusions|| |
While anemia is a major component of the GBD, its common place existence across most clinical practices across the world does not necessarily mean that it is easily and adequately evaluated and managed. It is important to keep in mind that any algorithmic guideline loses effectiveness when a patient is hospitalized, has multiple medical problems, or has undergone a recent RBC transfusion. In such situations, it can help referring to previous laboratory records, both for making a correct diagnosis, as also to provide the most cost-effectiveness. And, it should go without saying that judicious use of tests in most instances can provide all the information one needs, and at the same time keep costs within limits. 
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[Figure 1], [Figure 2]
[Table 1], [Table 2]