Classification of anemia
Reading File
Finding Sources
Searching PubMed
"anemia" AND "classification"
Reading File
Reading File
Reading File
Reading File
Reading File
Reading File
I now have excellent material from multiple authoritative sources. Let me compile the comprehensive answer.
Classification of Anemia
Anemia is defined as blood counts (hemoglobin/hematocrit) below the normal range for a given population. There are two major classification frameworks: morphological (by red cell size/MCV) and pathophysiological (by mechanism). These approaches are complementary and both are used in clinical practice.
1. Morphological Classification (by MCV)
Pioneered by hematologist Max Wintrobe, this approach classifies anemia by mean corpuscular volume (MCV). It is practical because it directly guides the diagnostic workup.
A. Microcytic Anemia (MCV < 80 fL)
Caused by any process that interferes with hemoglobin synthesis - less hemoglobin = smaller red cells.
| Cause | Mechanism |
|---|---|
| Iron deficiency anemia | Unable to synthesize heme |
| Thalassemia | Defective globin chain synthesis |
| Anemia of chronic disease/inflammation | Impaired iron delivery to RBC (cytokine-mediated) |
| Sideroblastic anemia | Defective heme synthesis (congenital or acquired) |
| Lead poisoning | Inhibits heme synthesis enzymes |
B. Normocytic Anemia (MCV 80-100 fL)
A broad category - includes early iron deficiency, anemia of chronic disease (most cases), and many systemic causes.
| Cause |
|---|
| Anemia of chronic disease / inflammation |
| Chronic kidney disease (EPO deficiency) |
| Aplastic anemia |
| Marrow invasion (leukemia, myeloma, granulomas) |
| Endocrinopathies (hypothyroidism, adrenal insufficiency, androgen deficiency) |
| Hemolytic anemias (sickle cell disease, autoimmune) |
| Pure red cell aplasia |
| Physiologic anemia of pregnancy |
| Anemia of the elderly |
C. Macrocytic Anemia (MCV > 100 fL)
Divided into two subtypes based on RBC shape:
Megaloblastic (Oval Macrocytes) - due to defective DNA synthesis:
- Vitamin B12 deficiency
- Folate deficiency
- Medications (chemotherapy agents, some antiepileptics)
- Myelodysplastic syndrome (MDS)
Non-megaloblastic (Round Macrocytes) - due to membrane defects:
- Alcohol use disorder
- Chronic liver disease
- Hypothyroidism
- Reticulocytosis (compensatory)
- Dysproteinemia
- Hypoxia, smoking
2. Pathophysiological Classification (by Mechanism)
Based on the underlying cause of the anemia. The reticulocyte count is the key first test - high reticulocytes = hyperproduction (loss/destruction); low/normal reticulocytes = underproduction.
A. Blood Loss
| Type | Examples |
|---|---|
| Acute | Trauma, surgical hemorrhage |
| Chronic | GI tract lesions (ulcers, carcinoma), gynecological (menorrhagia) |
B. Increased RBC Destruction (Hemolysis)
1. Intrinsic (Inherited) Defects:
- Red cell membrane disorders: Hereditary spherocytosis, hereditary elliptocytosis
- Enzyme deficiencies:
- Hexose monophosphate shunt: G6PD deficiency, glutathione synthetase deficiency
- Glycolytic pathway: Pyruvate kinase deficiency, hexokinase deficiency
- Hemoglobin abnormalities:
- Deficient globin synthesis: Thalassemia syndromes
- Structurally abnormal globins (hemoglobinopathies): Sickle cell disease, unstable hemoglobins
2. Extrinsic (Acquired) Causes:
- Immune-mediated: Autoimmune hemolytic anemia (warm/cold antibody), alloimmune (transfusion reactions, hemolytic disease of the newborn), drug-induced
- Microangiopathic hemolytic anemia (MAHA): HUS, TTP, DIC, defective cardiac valves
- Infections: Malaria, babesiosis
- Toxic/chemical injury
- Acquired genetic defects: Paroxysmal nocturnal hemoglobinuria (PNH) - deficiency of GPI-linked glycoproteins
- Sequestration: Hypersplenism
- Repetitive physical trauma: March hemoglobinuria, marathon running
C. Decreased RBC Production (Hypoproliferative)
1. Nutritional Deficiencies:
- Iron deficiency (impairs hemoglobin synthesis)
- B12 and folate deficiency (impair DNA synthesis)
- Copper, Vitamin C deficiencies
2. Bone Marrow Failure / Stem Cell Depletion:
- Aplastic anemia (acquired or inherited - Fanconi anemia, telomerase defects)
- Pure red cell aplasia (Diamond-Blackfan syndrome, parvovirus B19, immune-mediated)
- Transient erythroblastopenia of childhood (TEC)
3. Erythropoietin (EPO) Deficiency:
- Chronic kidney disease
- Anemia of chronic disease/inflammation (hepcidin-mediated iron sequestration + EPO resistance)
- Anemia of aging
4. Marrow Replacement (Myelophthisic Anemia):
- Hematological malignancies (leukemia, lymphoma, myeloma)
- Solid tumor metastases
- Granulomatous disease (TB, sarcoidosis)
- Myelofibrosis
5. Impaired Erythroblast Maturation:
- Thalassemia syndromes (also cause ineffective erythropoiesis)
- Myelodysplastic syndrome
Summary Table
| Classification | Key Test | Examples |
|---|---|---|
| Microcytic | Serum iron, ferritin, TIBC | IDA, thalassemia, sideroblastic |
| Normocytic | Reticulocyte count, peripheral smear | Aplastic, hemolytic, ACD |
| Macrocytic | B12/folate levels, peripheral smear | B12/folate def., liver disease |
| Blood loss | Clinical, stool guaiac | GI bleeding, trauma |
| Hemolytic | LDH, haptoglobin, Coombs | Spherocytosis, G6PD, AIHA |
| Hypoproliferative | Bone marrow biopsy | Aplastic, myelophthisic |
Sources: Harrison's Principles of Internal Medicine 22E (2025), p. 492 | Robbins, Cotran & Kumar Pathologic Basis of Disease, Table 14.1 | Tintinalli's Emergency Medicine, Table 144-2 | Goldman-Cecil Medicine, Table 144-9
This is a shared conversation. Sign in to Orris to start your own chat.