From the Guidelines
Red blood cell (RBC) indices are crucial for diagnosing and classifying different types of anemias, with the three main indices being Mean Corpuscular Volume (MCV), Mean Corpuscular Hemoglobin (MCH), and Mean Corpuscular Hemoglobin Concentration (MCHC). The MCV measures the average size of red blood cells, with normal values ranging from 80-100 femtoliters, and is used to classify anemias into microcytic (low MCV), normocytic (normal MCV), and macrocytic (high MCV) categories 1. For example, microcytic anemias often indicate iron deficiency or thalassemia, while macrocytic anemias may suggest vitamin B12 or folate deficiency, as noted in a study published in the Journal of the National Comprehensive Cancer Network 1. Key points to consider when evaluating RBC indices include:
- Microcytic anemia: may be caused by iron deficiency, thalassemia, anemia of chronic disease, or sideroblastic anemia 1
- Normocytic anemia: may be caused by hemorrhage, hemolysis, bone marrow failure, anemia of chronic inflammation, or renal insufficiency 1
- Macrocytic anemia: may be caused by vitamin B12 or folate deficiency, alcoholism, myelodysplastic syndrome (MDS), or certain drugs such as hydroxyurea or diphenytoin 1 The reticulocyte count and reticulocyte index (RI) are also important in evaluating the underlying mechanism of anemia, with a normal RI ranging between 1.0 and 2.0, and a low RI indicating decreased RBC production, while a high RI indicates normal or increased RBC production 1. Additionally, other tests such as iron and total iron binding capacity (TIBC), vitamin B12 and folate levels, stool guaiac, endoscopy, Coombs test, and kidney function tests may be necessary to determine the underlying cause of anemia, as discussed in a study published in the Journal of the National Comprehensive Cancer Network 1. It is also worth noting that a study published in MMWR Recommendations and Reports found that an RDW measurement can help determine the cause of a low MCV, with a low MCV and an RDW of greater than 14.0% indicating iron-deficiency anemia, whereas a low MCV and an RDW less than or equal to 14.0% indicates thalassemia minor 1. However, the most recent and highest quality study on this topic is from 2012, which provides a comprehensive review of the evaluation and treatment of anemia, including the use of RBC indices and other diagnostic tests 1.
From the Research
RBC Indices
RBC indices are used to classify anemia into different types, including microcytic, normocytic, and macrocytic anemia.
- Microcytic anemia is defined as anemia with a mean corpuscular volume (MCV) of less than 80 mcm3 in adults 2.
- The most common cause of microcytic anemia is iron deficiency anemia, which can be managed with oral or intravenous iron, depending on the severity and comorbid conditions of the affected individual 3, 2.
- Normocytic anemia has a broad differential, including nutritional deficiencies, blood loss, renal disease, malignancy, rheumatologic disorders, endocrine disorders, and other systemic diseases 4.
- Macrocytic anemias are seen with vitamin B12 and folate deficiency, alcohol use, thyroid disease, hydroxyurea, antiretroviral drugs, myelodysplastic syndromes, and myeloma 4.
Classification of Anemia
Anemia can be classified based on the mean corpuscular volume (MCV) into:
- Microcytic anemia (MCV < 80 mcm3)
- Normocytic anemia (MCV 80-100 mcm3)
- Macrocytic anemia (MCV > 100 mcm3) The classification of anemia guides the differential diagnosis and evaluation 4, 2.
Diagnostic Tests
Diagnostic tests for anemia include: