Erythrocyte Morphology and Its Disorders

*Ademola Samson Adewoyin, Oluwafemi Adeyemi, Nosimot Omolola Davies and Ann Abiola Ogbenna*

#### **Abstract**

Blood cell morphology is a key tool in laboratory haematology. Erythrocyte morphology points to possible aetiopathogenetic events in several primary and secondary haemopathies. Despite advances in medical technology and laboratory automation, red cell morphology remains a basic aspect of haematological evaluation. The human erythrocytes are discoid (bi-concave), about 7–8 μm (size of the nucleus of a small lymphocyte) in diameter, with a central area of pallor (which occupies a third of the red cell diameter) and is well haemoglobinised in the outer two thirds of the red cell diameters, without any inclusions. Deviations from the normal in terms of size, shape, colour, distribution or presence of inclusion bodies suggests possible disease processes. This chapter is therefore dedicated to morphologic description of the human erythrocytes, a study of possible abnormalities, its underlying pathophysiology and the associated differential diagnosis in humans.

**Keywords:** red cell, erythrocytes, morphology, haematology, red cell disorders, peripheral blood film

### **1. Introduction**

Erythrocytes are the major cellular component of the circulating blood. Roughly, erythrocytes in circulation average about 5 million cells per cubic millimetres of blood. With an average life span of about 100–120 days, erythrocyte production and senescence is maintained in constant equilibrium. Any imbalances affecting production or destruction of red cells result in red cell disorder. In essence, red cells are maintained at a constant volume in the body, depending on several factors. Physiologic factors such as age, sex, altitude, smoking status or pregnancy account for slight inter-individual and intra-individual variations. Typically, there are different measures of red cell counts and they include red cell mass, red cell volume, red cell count, haematocrit and haemoglobin concentration. Red cell volume or mass is expected to fall within an interval of mean ± 2 SD within a specified population for a person's age, sex and race.

Beyond count anomalies (quantitative abnormalities), morphologic aberrations (qualitative abnormalities) are highly relevant in clinical evaluation of red cell diseases. Normally, a red cell has a round form, shaped like a disc, well-haemoglobinised cytoplasmic rim with a central pallor covering inner third of the red cell. Deviations in morphology (size, shape, colour, contents/inclusion or distribution) may be associated or perhaps diagnostic of disease entities. For instance, a blood

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*Erythrocyte*

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picture with paucity of red cells, numerous red cell fragments, increased polychromatic red cells suggests a micro-angiopathy or fragmentation syndrome.

This chapter aims to discuss principles of red cell morphology, as well as describe red cells in terms of morphology, identify morphologic abnormalities associated with different disease conditions.
