Overview of Morphologic Evaluation
- Blood smear examination constitutes an essential primary diagnostic step in anemia evaluation.
- Classifies anemia morphologically (microcytic, normocytic, macrocytic).
- Identifies specific red blood cell (RBC) shape abnormalities (poikilocytosis) and size variations (anisocytosis) guiding targeted investigations.
Findings by Anemia Etiology
Nutritional Anemias
Iron Deficiency Anemia (IDA)
- RBC Morphology: Microcytic and hypochromic.
- Variation: Pronounced anisocytosis and poikilocytosis.
- Specific Shapes: Few ovalocytes and teardrop cells present.
- Associated Findings: Thrombocytosis commonly observed.
Megaloblastic Anemia (B12/Folate Deficiency)
- RBC Morphology: Macrocytic; predominantly macro-ovalocytes.
- Variation: Marked anisocytosis and poikilocytosis.
- Inclusions: Teardrop cells, Cabot rings, Howell-Jolly bodies, and punctate basophilia.
- Associated Findings: Hypersegmented neutrophils (>5 lobes) pathognomonic. Giant metamyelocytes present.
Hemoglobinopathies & Thalassemias
Thalassemia Syndromes
- Thalassemia Trait: Marked hypochromia, microcytosis, target cells, fine basophilic stippling.
- Thalassemia Major: Severe hypochromia, extreme microcytosis, massive anisocytosis.
- Specific Features: Fragmented RBCs, teardrop cells, numerous nucleated RBCs, polychromatophilia.
Sickle Cell Disease (HbSS)
- RBC Morphology: Sickled cells (irreversibly sickled cells), target cells.
- Inclusions: Howell-Jolly bodies (indicating functional hyposplenism), nucleated RBCs.
- Associated Findings: Polychromasia (reflecting reticulocytosis), neutrophilia.
Hemoglobin C & E Diseases
- HbC Disease: Numerous target cells, occasional spherocytes. Characteristic intracellular rhomboidal hemoglobin crystals.
- HbE Disease: Microcytosis, hypochromia, prominent target cells.
Red Cell Membrane & Cytoskeleton Defects
Hereditary Spherocytosis
- RBC Morphology: Spherocytes (hyperchromic, spherical, lack central pallor).
- Size: Microspherocytes typical. Low-normal MCV, elevated MCHC.
- Associated Findings: Polychromatophilic reticulocytes.
Hereditary Elliptocytosis & Pyropoikilocytosis
- Hereditary Elliptocytosis (HE): Normochromic, normocytic elliptocytes (cigar-shaped) comprising 25-90% of cells.
- Hereditary Pyropoikilocytosis (HPP): Extreme microcytosis (MCV 50-65 fL). Extraordinary variation in size/shape. Bizarre poikilocytes, RBC fragments, budding red cells, microspherocytes.
Hereditary Stomatocytosis & Acanthocytosis
- Stomatocytosis: Stomatocytes exhibit linear, slit-like central pallor (bowl-shaped in 3D). Associated with macrocytosis.
- Acanthocytosis: Acanthocytes (spur cells) demonstrate irregular, thorn-like spicules. Seen in abetalipoproteinemia and severe liver disease.
Erythrocyte Enzymopathies
Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency
- Acute Hemolysis: “Bite cells” (degmacytes) and blister cells.
- Inclusions: Heinz bodies (precipitated denatured hemoglobin) visible only with supravital stains (e.g., brilliant cresyl blue), not Wright stain.
Pyruvate Kinase (PK) Deficiency
- RBC Morphology: Echinocytes (burr cells), contracted spiculated pyknocytes.
- Associated Findings: Polychromatophilia and macrocytosis reflecting extreme reticulocytosis.
Microangiopathic Hemolytic Anemias (MAHA)
- Etiologies: Hemolytic-Uremic Syndrome (HUS), Thrombotic Thrombocytopenic Purpura (TTP), Disseminated Intravascular Coagulation (DIC).
- RBC Morphology: Schistocytes (RBC fragments), helmet cells, burr cells, triangular shapes, microspherocytes.
Summary of Specific Erythrocyte Morphologies
| Morphologic Finding | Pathophysiologic Description | Key Differential Diagnoses |
|---|---|---|
| Target Cells | Increased surface-to-volume ratio | Thalassemia, HbC/HbE disease, Liver disease, Severe iron deficiency, Asplenia, Abetalipoproteinemia. |
| Spherocytes | Decreased surface-to-volume ratio, hyperdense | Hereditary spherocytosis, Autoimmune hemolytic anemia, ABO incompatibility, Burns, Hypersplenism. |
| Schistocytes | Helmet/triangular fragments from vascular impact | MAHA (DIC, HUS, TTP), Kasabach-Merritt syndrome, Artificial heart valves, Severe burns. |
| Acanthocytes | Irregular, wide-based spicules (spur cells) | Liver disease, Abetalipoproteinemia, Hypothyroidism, Post-splenectomy. |
| Echinocytes | Evenly distributed short spicules (burr cells) | Renal failure, PK deficiency, Liver disease, Dehydration, Artifact. |
| Teardrop Cells | Dacrocytes; stretched during marrow exit | Thalassemia major, Myelofibrosis, Bone marrow infiltration, Leukoerythroblastic reaction. |
| Elliptocytes | Oval or cigar-shaped erythrocytes | Hereditary elliptocytosis, Iron deficiency, Megaloblastic anemia, Sickle cell trait/disease. |
| Basophilic Stippling | Aggregated ribosomal RNA (coarse or fine) | Lead poisoning (coarse), Thalassemia (fine), Hemolytic anemias, Iron deficiency. |
| Howell-Jolly Bodies | Densely stained nuclear DNA remnants | Asplenia/Hyposplenia, Sickle cell disease, Megaloblastic anemia, Severe IDA. |
| Nucleated RBCs | Immature RBCs escaping marrow prematurely | Severe hemolysis (Thalassemia, Sickle cell), Hypoxia, Acute bleeding, Leukoerythroblastic reaction. |