MORPHOLOGICAL VARIATIONS ABNROMALITIES IN RED BLOOD CELLS (ERYTHROCYTES)

MORPHOLOGICAL VARIATIONS/ ABNROMALITIES IN ERYTHROCYTES

MORPHOLOGICAL VARIATIONS/ ABNROMALITIES IN ERYTHROCYTES-Alterations in the morphology of erythrocytes are associated with many diseases. The most significant of these conditions is anaemia, in which the oxygen carrying capacity of blood is decreased. The causes of anaemia are varied, and most of them are expressed as changes in RBC morphology. Therefore, morphological examination of red cells is very helpful in evaluating and determining the cause of anaemia.

Normal red blood cells stained with a Romanowsky stain are nearly uniform in size, shape and colour. Each cell appears as a pink disk, about 7 microns in diameter, with a rim of haemoglobin and a clear central area called central pallor. The central pallor generally occupies less than one-third of the cell. The red cells having normal size and normal colour are said to be normocytic and normochormic. Blood disorders may also be indicated by changes in the shape of red cells or by the presence of inclusions. Figure 4.4 shows some red cell abnormalities and inclusions.

During the examination of the peripheral blood smear, the following characteristics in the red cell morphology should be observed and reported:

1. Colour (Haemoglobin content)

2. Size 

3. Shape

4. Inclusions

5. Distribution pattern

6. Nucleated red cells

7. Artefacts.

1. Variation in Colour:-A red cell showing a normal staining reaction is described as normochromic and represents a haemoglobin content within the normal range.

Hypochromic cells stain very pale and show an increased area of central pallor. Hypochromasia is a result of reduced haemoglobin content, most commonly observed in iron-deficiency anaemia.

Hyperchromic cells are not seen very commonly. These cells stain deeply appearing oversaturated with haemoglobin. Such cells are observed in spherocytosis.

Polychromatic cells show a mixed staining reaction and appear blue-orange in colour. They contain residual ribonucleic acid (RNA) which is basophilic, in addition to haemoglobin. These are slightly premature cells, just released in circulation from the bone marrow.

A normal blood smear may show 1-2 % polychromatic cells. They are called reticulocytes. They are slightly larger in size than normal red cells. When stained with a supra-vital stain such as brilliant cresyl blue, these cells show a reticulum of RNA. An increase in the number of these cells in the peripheral blood indicates increased red cell production by the bone marrow and may be seen in conditions such as haemolytic anaemia.

2. Variation in Size:- Variation in size, called anisocytosis, is a common and important erythrocyte morphological feature. The term describes any large variation in size of a normal erythrocyte. A red cell within the normal range of diameter is called a normocyte.

 Macrocytosis:_ It is a condition in wnich red blood cells have a diameter greater than 7.8 microns and MCV usually greater than 100 cu.microns (femtolitres, fL). Macrocytic cells are characteristically seen in megaloblastic anaemia due to Vit B12 or folic acid deficiencies, or in haemolytic anaemia. 

Microcytosi:-s It is a condition in which red blood cells have a diameter less than 6.5 microns and MCV less than 80 cu microns(fL). Microcytic cells frequently have less haemoglobin than normal cells and are seen in iron deficiency anaemia, spherocytic anaemia, lead poisoning and thalassaemia.

3. Variation in Shape:-A normal red cell is a circular, biconcave disc. Any alteration in this shape should be observed.

Poikilocytosis:-  The term describes a condition in which there are major variations in the shape of the erythrocyte. The most common of these variations is a tear drop shape. They are found in various anaemias and haemolytic states.

Spherocyte:- It is a red cell whose average thickness has increased, usually with a reduced diameter. The spherical shape results when a normal cell volume is enclosed within a reduced surface area. When seen in a blood smear, it is a small, deeply staining cell with no red cell central pallor. A spherocyte has a 14 day life span as compared to 120 days of a normal blood cell. It commonly shows in creased osmotic fragility. Spherocytes are found in congenital and acquired haemolytic anaemias.

Elliptocytes :- These are red blood cells which are oval or egg-shaped, sometimes almost cylindrical. They do not show the central pallor. Large elliptocytes may be seen in megaloblastic anaemias. Elliptocytosis may be acquired or inherited

.

Target cells:- These cells have a central area of haemoglobin within the area of central pallor, making them look like targets. This is a result of having excessive cell membrane, compared to the amount of haemoglobin. They occur in various types of anaemias, liver disease and after splenectomy.

Sickle cells:-These elongated erythrocytes with crescentic shapes and occasionally U, S, or L shapes are formed after exposure to reduced oxygen tension. This variation occurs if the red blood cell contains the abnormal haemoglobin S. This is a hereditary disorder, which may appear in two forms: the sickle cell trait or sickle cell disease. 

Burr cells:- These erythrocytes have a focal crenation producing irregular contractions resulting in long spine-like processes, irregularly distributed over the cell surface. They have been observed in renalinsufficiency and thrombocytopenia.

Schistocytes:- These are fragmented portions of red cells which appear in various shapes, e.g., helmet cells. Their presence indicates a very serious pathological condition e.g. mechanical fracture of cells during circulation in conditions such as a defective heart valve and glomerular filtration. They may also form due to toxic or metabolic injury as in malignancies. They are frequently seen in blood smears of severely burnt patients, and in some haemolytic anaemias.

Acanthocytes:- These cells show irregular margins with pointed projections. The cause of this variation is not clearly understood, but may be due to an abnormality in the phospholipid content of the red cell membrane.

Table 4.3 shows causes of variations in shape, size and colour of red cells.

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4. Abnormal Inclusions in Red Blood Cells:- A normal red cell does not contain any inclusion. Various types of inclusions may be seen in RBCS which may indicate disorders or disease condions. Basophilic stippling The red cells may show fine or coarse dark blue granules dispersed throughout the cell. This is known as basophilic stippling and results from the precipitation of ribosomal RNA.

The stippling may occur due to abnormal red cell formation in the bone marrow and is seen in heavy metal poisoning (lead, mercury or bismuth), thalassaemia and megaloblastic anaemia. Howell-Jolly bodies- These are round, dense purple granules less than 1 micron in size, appearing eccentrically located in some red cells. If present, not more than two Howell-Jolly bodies are seen in a single red cell. They are the remnants of the nuclear material and indicate incomplete expulsion of the nucleus from the red cell through the spleen. Therefore, the Howell-Jolly bodies may appear in the peripheral blood after splenectomy, and also in megaloblastic anaemia and some haemolytic anaemias.

Heinz bodies:- Heinz bodies are oxidised denatured haemoglobin. They can be demonstrated only by supravital staining with brilliant cresyl blue. Heinz bodies my appear in the peripheral blood smear after removal of the spleen, or in haemolytic anaemias such as that due to G6PD deficiency.

Siderocytes:- The red cells containing small, dense, blue-purple granules are called siderocytes. They resemble Howell-Jolly bodies in appearance, but they are granules of free iron, uncombined with haemoglobin, instead of fragments of DNA. The iron-granules inside siderocytes are known as Pappenheimer bodies. A special stain for iron, such as Prussian blue, can distinguish these granules from Howell-Jolly bodies. They are seen in peripheral blood after the removal of spleen.

Cabot's rings:- These are rare inclusions appear ing as threadlike strands in the form of a ring or figure of 8, reddish-violet in colour. Their origin is not clearly understood, but may be the result of anabnormality in mitosis. They appear in cases of megaloblastic anaemia or lead poisoning. They can be differentiated from the malarial ring forms by their large size and absence of red chromatin.

Parasites:- Various stages of the malarial parasites may be seen in the red cells of patients suffering from malaria. Their appearance depends on the developmental stage (e.g. ring form, amoeboid trophozoite, schizont, gametocyte) and the infecting species of the genus Plasmodium, e.g., Plasmodium vivax, Plasmodium falciparum. Other parasites such as trypanosomes and microfilariae may also be seen in a peripheral blood smear. Blood parasites are discussed in greater details in Parasitology in Microbiology Section.

5. Alterations in the Distribution Pattern of Red Cells

Rouleaux Formation:- Sometimes red cells stick together in row looking like stacks of coins. This is called rouleaux formation. They may appear in the thick portion of the smear of healthy individuals. However, their presence in the thinner 'examination area of the smear indicates increased levels of plasma globulin or fibrinogene.g. in multiple myeloma 

Agglutination:- Agglutination is irregular clumping. If agglutination is observed in blood samples stored in the refrigerator, it may be due to the presence of cold agglutinins, which are autoantibodies indicating an auto-immune haemolytic state or anaemia.

6. Nucleated red Cells in the Peripheral(Blood (Erythroblastic Reaction):-The peripheral blood of a healthy individual does not show the presence of nucleated red cells. Their appearance in the peripheral blood indicates intense stimulation of the bone marrow releasing red cell precursors in the peripheral blood. This occurs in acute blood loss, megaloblastic and haemolytic anaemias and malignancies Normoblasts (erythroblasts) in various stages of development may be seen depending on the severity of the stimulus.

7. Artefacts in Red Cells:- Platelets on top of a red cell, punched-out red cell or stain deposits may appear as variations in red cell morphology . they should not they should be confused with red cell abnormalities.