From the Guidelines
The workup for microcytic anemia should begin with a complete blood count (CBC) with peripheral smear, iron studies, and hemoglobin electrophoresis to evaluate for iron deficiency and hemoglobinopathies, as recommended by the British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults 1. The initial evaluation should include measurements of mean cell Hb (MCH) and mean cell volume (MCV) to confirm the presence of microcytosis and hypochromia, which are characteristic of iron deficiency anemia.
- Key laboratory tests include:
- Serum iron, total iron binding capacity (TIBC), transferrin saturation, and ferritin to assess iron stores and deficiency
- Hemoglobin electrophoresis to evaluate for hemoglobinopathies like thalassemia, particularly in patients with Mediterranean, African, or Asian ancestry
- Reticulocyte count to assess bone marrow response
- Inflammatory markers (ESR, CRP) to evaluate for anemia of chronic disease
- Stool occult blood testing to screen for gastrointestinal bleeding, a common source of iron loss
- In patients with microcytosis and normal iron studies, Hb electrophoresis is recommended to evaluate for hemoglobinopathies, particularly if there is an appropriate ethnic background 1.
- The workup should be tailored based on the patient's history, physical examination findings, and initial laboratory results, with treatment directed at the underlying cause.
- For patients over 50 or with concerning symptoms, endoscopic evaluation (colonoscopy and/or upper endoscopy) may be necessary to identify a source of bleeding, as recommended by the practice guidelines for the diagnosis and management of microcytic anemias due to genetic disorders of iron metabolism or heme synthesis 1.
From the Research
Workup for Microcytic Anemia
The workup for microcytic anemia involves several steps to determine the underlying cause of the condition.
- The initial step is to measure the mean corpuscular volume (MCV) to confirm the presence of microcytosis, which is typically defined as an MCV of less than 80 µm3 (80 fL) in adults 2.
- The next step is to measure serum ferritin levels, which is the first laboratory test recommended in the evaluation of microcytosis 2.
- Low ferritin levels suggest iron deficiency, while normal or elevated levels may indicate other causes of microcytosis, such as thalassemia or anemia of chronic disease 2, 3.
- Further evaluation may include measurement of total iron-binding capacity, transferrin saturation level, serum iron level, and possibly hemoglobin electrophoresis 2, 4.
- The erythrocyte size-distribution width may be helpful in distinguishing iron deficiency from thalassemia minor 4.
- Examination of the peripheral smear and bone marrow evaluation may also be necessary to confirm the diagnosis and determine the underlying cause of microcytosis 5, 6.
Laboratory Tests
The following laboratory tests may be used to evaluate microcytic anemia:
- Serum iron level
- Total iron-binding capacity
- Serum ferritin level
- Transferrin saturation level
- Hemoglobin electrophoresis
- Erythrocyte size-distribution width
- Peripheral smear examination
- Bone marrow evaluation
Underlying Causes
The underlying causes of microcytic anemia include:
- Iron deficiency anemia, which is the most common cause of microcytosis 5, 2, 3
- Thalassemia, which is a genetic disorder that affects the production of hemoglobin 2, 6
- Anemia of chronic disease, which is a condition that occurs in response to chronic inflammation or infection 2, 3
- Sideroblastic anemia, which is a rare disorder that affects the production of hemoglobin 5, 6
- Lead toxicity, which can cause microcytosis and anemia 2