Anisocytosis versus poikilocytosis
Anisocytosis is marked variation in red cell size, while poikilocytosis is variation in red cell shape.
Remember
Anisocytosis is variation in red cell size and poikilocytosis is variation in red cell shape, so sort the red cell terms into size, shape and colour.
A blood film is a thin layer of blood on a glass slide that is stained and looked at under a microscope. In a healthy person the red cells are similar in size, and each has a pale centre, called central pallor.
In anisocytosis, small and large red cells appear side by side in the same field. Poikilocytosis is variation in the shape of red cells, such as teardrop, sickle or fragmented forms. A film can show several changes at once, because many disorders alter size, shape and colour together, so the skill is to choose the term that matches the main finding.
The other red cell terms each name one feature. Microcytosis means that the cells are small, and macrocytosis means that they are large. Hypochromia means that the cells look pale, because the central pale area is enlarged and the cells contain less haemoglobin. Polychromasia is a blue-grey tint to the cytoplasm. Sorting the terms into size, shape and colour groups makes them much easier to remember.
Anisocytosis is common and non-specific, which means that it does not give a diagnosis by itself. It tells the reader to look for the cause, and it is seen in many anaemias. The same finding appears as a raised red cell distribution width (RDW), the number that measures how much red cell size varies.
Key facts
- Anisocytosis
- marked variation in red cell size, with small and large cells side by side in the same field.
- Poikilocytosis
- variation in the shape of red cells, for example teardrop, sickle or fragmented forms.
- Red cell distribution width (RDW)
- the number that measures how much red cell size varies, and it is raised when anisocytosis is present.
- Hypochromia
- pale red cells, because the central pale area is enlarged, which points to too little haemoglobin.
- Microcytosis
- red cells that are small, which is a different finding from marked variation in size.
- Polychromasia
- a blue-grey tint to the red cells, which is a change in colour and not in size.
Exam traps
- Poikilocytosis does not describe red cells that differ in size, because it names variation in shape, such as teardrop, sickle or fragmented forms.
- Cells with preserved central pallor are not hypochromic, because hypochromia means that the central pale area is enlarged by less haemoglobin.
- Microcytosis is not the same as anisocytosis, because a population of red cells can be small yet uniform, which is different from marked variation in size.
Read the full notes
Tested in 6 SimpleMed+ questions
Practice it in Haematology, with the answer and a full explanation after every question.
Practice these questions