Poikilocytosis
February 15th, 2021
On this page:ElliptocytosisMacroovalocytesSpherocytosisMicrospherocytosisKeratocytes / PrekeratocytesSchistocytesAcanthocytesEchinocytesStomatocytesTarget CellsTeardrop CellsSickle Cells
Overview
Poikilocytosis refers to the presence of abnormally shaped red blood cells on a blood film. There are a wide variety of red cell morphological changes which may suggest various hereditary or acquired conditions.
Elliptocytosis
Elliptocytes are elongated cells. These are often also called ovalocytes.
Causes of Elliptocytosis
- Hereditary elliptocytosis
- Iron deficiency anaemia
- Thalassaemia
- Primary myelofibrosis
Macroovalocytes
Macroovalocytes are large (>100fL) oval-shaped cells, and are suggestive of megaloblastic anaemia.
Spherocytosis
Spherocytes are round cells with loss of central pallor.
This occurs due to a reduction in the cell membrane size without a reduction in the size of the cytoplasm, which may occur due to direct damage or removal of a portion of the cell membrane by phagocytes.
Causes of Spherocytosis
- Hereditary spherocytosis
- Immune haemolysis - warm autoimmune haemolytic anaemia, cold agglutinin haemolysis, transfusion reaction, haemolytic disease of the newborn, drug-induced haemolysis
- Clostridium infection
- Severe burns
- Snake bite
Red cells have a spherocytoid appearance in the thinner part of the blood film, so it is important to look at a blood film in the area where red cells are first starting to touch.
Microspherocytosis
Microspherocytes are small round cells with loss of central pallor (essentially spherocytic schistocytes).
Causes of Microspherocytosis
- Hereditary spherocytosis
- Microangiopathic haemolytic anaemia
- Burns
Keratocytes / Prekeratocytes
Prekeratocytes and keratocytes are blood film findings that are suggestive of oxidative haemolysis.
Keratocytes (bite cells) are red cells with a bite-like defect in their membrane. These occur due to phagocytosis of a Heinz body (made up of denatured haemoglobin), leaving a bite in the cell.
Prekeratocytes (blister cells) are similar to keratocytes, however retain a sliver of cell membrane - leaving the cell with a defect that resembles a blister.
Causes of Keratocytes / Prekeratocytes
- Glucose-6-phosphate dehydrogenase (G6PD) deficiency
- Unstable haemoglobins
- Drug-induced oxidative haemolysis
Schistocytes
Schistocytes are small irregular fragments of red blood cells of varying shapes. Their presence on blood films is suggestive of microangiopathic haemolytic anaemia, and should be diagnosed rapidly as many of its causes are life-threatening.
Causes of Schistocytosis
- Microangiopathic haemolytic anaemia - TTP, HUS, aHUS, DIC, preeclampsia / HELLP syndrome, SLE, malignant hypertension, brown snake bite
- Mechanical haemolysis - valvular leaks, cardiac prostheses, renal replacement, ECMO, march haemoglobinuria
- Myelodysplastic syndrome
Acanthocytes
Acanthocytes, also known as spur cells, are red blood cells with irregular membrane projections.
Acanthocytosis may be congenital or acquired, and is classically associated with spur cell haemolytic anaemia in the context of alcoholic cirrhosis.
Causes of Acanthocytes
- Hereditary acanthocytosis
- Spur cell haemolytic anaemia (liver disease) - particularly with alcoholic cirrhosis
- Hypobetalipoproteinaemia - hereditary, malnutrition
- Post splenectomy
Echinocytes
Echinocytes, also known as burr cells, are red blood cells with short and evenly spaced projections.
Echinocytes are most commonly artefactual, however may occur with certain congenital conditions or with severe liver disease.
Causes of Echinocytosis
- Processing artefact - due to prolonged storage in EDTA
- Pyruvate kinase deficiency
- Liver cirrhosis
Stomatocytes
Stomatocytes, also known as mouth cells, contain a central slit of pallor (like a mouth) due to overhydration of the cell.
Causes of Stomatocytosis
- Hereditary stomatocytosis
- Alcohol abuse
- Rh null phenotype
- Hypoalphalipoproteinaemia
Target Cells
Target cells, also known as codocytes, have normal central pallor with an added area of dark red discolouration in the very centre.
Causes of Target Cells
- Liver disease (obstructive or intrahepatic)
- Haemoglobinopathies
- Beta thalassaemia
- Iron deficiency anaemia
- Sideroblastic anaemia
- Sickle cell anaemia
- Post splenectomy
- Lead poisoning
Teardrop Cells
Teardrop cells, also known as dacrocytes, have an abnormal teardrop-like shape.
Teardrop cells are classically suggestive of myelofibrosis, though may also occur with severe red cell dysplasia.
Causes of Teardrop Cells
- Myelofibrosis (primary or secondary)
- Megaloblastic anaemia - B12 / folate deficiency, drug-induced
- Myelodysplastic syndrome
- Thalassaemia major
Sickle Cells
Sickle cells, also known as drepanocytes, are crescent-shaped cells caused by aggregation of haemoglobin S.
Sickle cells are a pathognomonic finding of sickle cell disease.
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