Red cell morphology on the smear
- Topic
Red cell shapes and inclusions are clues: each abnormal form points to a small set of diseases.
What it is
A normal red cell is a biconcave disc with central pallor about a third of its diameter. Damage to the membrane, the haemoglobin, the marrow or the spleen changes the shape or leaves inclusions. Reading the smear turns these shapes into a short differential diagnosis and often points to the mechanism: membrane loss (spherocytes), mechanical cutting (schistocytes), excess membrane (target cells), polymerized haemoglobin (sickle cells), squeezing through a fibrotic marrow (teardrops) or splenic removal of inclusions (bite cells).
Abnormal red cells and what they suggest
| Cell | What it looks like | Mechanism | Main causes |
|---|---|---|---|
| Spherocyte | Small, dense, no central pallor | Loss of membrane | Hereditary spherocytosis, warm autoimmune haemolysis |
| Schistocyte | Fragments, helmets, triangles | Cut by fibrin strands or turbulence | TTP, HUS, DIC, mechanical valves |
| Target cell | Central dark spot inside pallor | Excess membrane relative to haemoglobin | Thalassaemia, haemoglobin C, liver disease, asplenia |
| Sickle cell | Crescent or holly-leaf shape | Polymerized deoxygenated HbS | Sickle cell disease |
| Teardrop cell (dacrocyte) | Single tapered tail | Deformed leaving a fibrotic or infiltrated marrow | Myelofibrosis, metastatic cancer in marrow |
| Bite cell | Bite-shaped notch | Splenic removal of Heinz bodies | G6PD deficiency, oxidant drugs |
| Howell–Jolly body | Small round dark dot | Nuclear remnant not removed by the spleen | Asplenia, sickle cell disease |
| Basophilic stippling | Fine blue dots | Persisting ribosomal RNA | Lead poisoning, thalassaemia |
| Pencil cell | Long thin elliptical cell | Iron-deficient erythropoiesis | Iron deficiency anaemia |
Clinical notes
- Schistocytes with thrombocytopenia are an emergency clue to thrombotic microangiopathy.
- Rouleaux (stacked coins) suggest high immunoglobulin levels such as myeloma.
In the lab
- Automated analysers give size and colour; only the smear shows shape and inclusions.
- Supravital stains show reticulocytes and Heinz bodies; Prussian blue shows siderocytes and ring sideroblasts.
Test yourself
Think of the answer, then tap the question to see it.
Which red cell finding indicates a missing or nonfunctioning spleen?
Howell–Jolly bodies (nuclear remnants), often with target cells.
What produces bite cells?
Splenic macrophages remove Heinz bodies (denatured haemoglobin) from oxidant-damaged red cells, as in G6PD deficiency.
Which disorders give schistocytes?
Microangiopathic haemolysis (TTP, HUS, DIC, malignant hypertension) and mechanical heart valves.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Hemolytic anemia: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Anemia | MedlinePlus (MedlinePlus, US National Library of Medicine, 2026).
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Representative model, for educational purposes only.