Approach Considerations
Measurement of red blood cell (RBC) indices and examination of peripheral blood smear are critical in the workup of anemia. Bone marrow examination may be extremely valuable, but is not necessary in all patients.
Additional laboratory tests that allow differentiation of anemias based on RBC index information include the following:
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Serum iron concentration
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Total iron-binding capacity (TIBC)
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Serum vitamin B12
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Serum folate
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Serum bilirubin
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Liver function tests (LFTs)
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Thyroid panel
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Hemoglobin (Hgb) electrophoresis
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Heavy metal studies
The ultimate diagnosis of chronic anemia is based on results of blood studies. In the initial emergency department (ED) evaluation, a prudent choice of labs includes the following:
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Complete blood count (CBC) with leukocyte differential and peripheral smear
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RBC indices
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Reticulocyte count
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Bilirubin
Based on the RBC indices, further blood work may be initiated in the ED. Iron studies may be performed. These can include ferritin, TIBC, total iron, and percent saturation. Typically, iron studies are helpful in the diagnosis of microcytic and normocytic anemias.
Serum vitamin B12, folate levels, and the RBC folate level are useful in evaluating macrocytic anemias. Order concurrent liver and thyroid function studies for patients with macrocytic anemia.
Hgb electrophoresis may delineate sickle cell anemia and thalassemias.
Heavy metal studies (eg, serum lead level) may be considered when a high level of suspicion is present, historically and clinically, for heavy metal poisoning.
Point-of-care technologies are emerging as a portable and convenient method of screening for anemia. These technologies include noninvasive screening with a near-infrared photoplethysmography smartphone, and minimally invasive screening with microfluidic devices that can detect the level of hemoglobin in a few drops of capillary blood using optical absorbance. [5]
Imaging studies
No specific imaging tests exist for chronic anemia; however, several imaging modalities can be used in examining the underlying etiology (eg, computed tomography [CT] scanning for abdominal mass, chest radiography for histoplasmosis/coccidioidomycosis).
Bone marrow examination
Bone marrow examination may be diagnostic in cases in which workup is otherwise nonspecific. This is not a procedure performed in the acute setting.
Common Lab Studies
Hematocrit
The hematocrit, or packed cell volume (PCV), indicates the percentage of RBCs in a volume of whole blood. Increased values occur with severe dehydration, erythrocytosis, polycythemia, severe burns, and shock, and in people living at high altitudes, males, and infants.
Decreased values occur with anemia and the many differential diagnoses that encompass anemia (eg, hyperthyroidism, leukemia, liver disease, hemolytic reactions). Other causes of decreased hematocrit values include female sex, advanced age, and pregnancy. Hematocrit value is not reliable immediately after blood loss or blood transfusions.
Hemoglobin concentration
Hgb concentration is expressed in grams per 100 mL of blood. Each gram of Hgb has a carrying capacity of 1.34 mL of oxygen.
Increased Hgb values can indicate severe dehydration, erythrocytosis, polycythemia, severe burns, shock, chronic obstructive pulmonary disease (COPD), or congestive heart failure (CHF). Increased values also occur in people living in high altitudes, people taking drugs such as gentamicin or methyldopa, and infants.
Decreased values indicate anemia and the many differential diagnoses that encompass anemia (eg, hyperthyroidism, leukemia, liver disease, hemolytic reactions). Other possible causes of decreased Hgb values include the following:
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Overhydration
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Pregnancy
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Drugs (eg, acetaminophen, antineoplastic agents, chloramphenicol, hydralazine, monamine oxidase inhibitors [MAOIs], nitrites, penicillin, tetracycline, sulfonamide)
Mean corpuscular volume
Mean corpuscular volume (MCV) is the hematocrit divided by the RBC count. It is a measurement of the volume occupied by a single RBC and is an indicator of individual cell size. Increased values indicate differentials that encompass macrocytic anemia (eg, vitamin B12 or folate deficiency, liver disease, alcoholism), while decreased values indicate microcytic anemia (ie, iron deficiency, thalassemia, anemia of chronic blood loss). This is the most important of the RBC indices. A normal value can appear when a wide variety of cell sizes is present (ie, macrocyte and microcyte).
Mean corpuscular hemoglobin concentration
Mean corpuscular Hgb concentration (MCHC) is the Hgb divided by the hematocrit. It represents the average concentration of Hgb in the RBCs. The value is expressed as a percentage. Increased values point to spherocytosis (eg, congenital hemolytic anemia), and decreased values indicate iron deficiency, thalassemia, or macrocytic anemia.
Mean corpuscular hemoglobin
Mean corpuscular Hgb (MCH) is the Hgb divided by the RBC count. It represents the average weight of Hgb in the RBCs and serves to confirm the accuracy of MCV value. Increased values occur in macrocytic anemia, newborns, and infants. Decreased values indicate microcytic anemia.
Reticulocyte count and index
The first question a clinician must address is whether the anemia is due to a decreased production of RBCs or to increased destruction or loss of RBCs. The reticulocyte count is the most valuable test in answering this question.
A reticulocyte is a nonnucleated, immature RBC; reticulocytes develop into mature RBCs within1-2 days after they are released from the bone marrow into the peripheral blood. [6] Reticulocytes normally constitute 0.5 to 2.5%.Increased values indicate accelerated erythropoiesis and can be present following treatment of anemia, after splenectomy, 3-4 days following hemorrhage, in sickle cell disease hemolytic anemia, during pregnancy, or in infants. Decreased values indicate decreased RBC production by the bone marrow and can be a result of aplastic anemia, chronic infection, or radiation therapy. A persistent reticulocyte deficiency is a poor prognostic sign.
The reticulocyte index (RI) is defined as the reticulocyte count divided by 2 and then multiplied by the ratio of the patient's hematocrit (or Hgb) to normal hematocrit (or Hgb). Good marrow response is defined as an RI value of 2-6.
