Hypochromic Microcytic Anaemia
Shown above is an image of hypochromic microcytic anaemia. This patient had iron deficiency anaemia. Microcytosis is presence of small erythrocytes and hypochromia presence of erythrocytes that are poorly haemoglobinized. The nucleus of a small lymphocyte, the cell in the centre of the image, is a good guide to the size of erythrocytes on a peripheral smear. The nucleus has a diameter of 8.5 µm and a normal erythrocyte a diameter of 7.5 µm. The erythrocytes in in the image are substantially smaller than the lymphocyte nucleus. Erythrocytes have a central pale staining area which occupies about one third of erythrocyte diameter. As the cells get less haemoglobinized the central pale staining area increases. Many of the erythrocytes in the image above have a pale staining area occupies all but a thin rim at the periphery. In others, the pale staining area is increased. The erythrocyte sizes vary. Anisocytosis, increased variation in erythrocyte size, a feature of iron deficiency anemia, is evident in the image.
Lymphocytes – Large and Small
There are two types of lymphocytes small (10-12µm) and large (12-16µm).
Most of the lymphocytes in the peripheral blood are small. The nucleus of he lymphocytes is small, round, usually indented. The chromatin of the lymphocyte nucleus
- Deep purple, small, round, usually indented
- Has no nucleoli
- Has a densely clumped deep chromatin
The cytoplasm of the lymphocyte is
- Moderately basophilic (blue)
- Scanty forming a thin rim around the nucleus
- Devoid of granules
Large lymphocytes have a more abundant cytoplasm with a few azurophilic granules. Some of these are T supressor lymphocytes (Cd3+ Cd8+) while others are NK cells (Cd3 – CD8+). The picture above shows a large granular lymphocyte
Figure 1. Two Monocytes
Monocytes are the largest leucocytes. They vary considerable in size and shape and may measure about 12-20 µm in diameter. The have a lobulated nucleus that is centrally placed with a fine chromatin. The nucleus has been classically described as kidney shaped but may take other lobulated forms. The cytoplasm is abundant, grey or light-blue grey. Fine azurophilic granules that are seen on staining on wright’s stain giving the cytoplasm a ground glass appearance (evident in the monocyte on the left in figure 1). The granules may become prominent in patients with marrow stimulation (bacteraemia, marrow recovery from aplasia or following the use of G-CSF)
Monocytes show typical granules in some inherited disorders. They are phagocytic and may show ingested red cells, malarial pigment or microorganisms.
Figure 2. Neutrophilic Myelocyte and Metamyelocyte- The cell on the left is a myelocyte and the right is a metamyelocyte. Compared to a monocyte (figure 1) a metamyelocyte has a coarser chromatin and pink cytoplasm with fine pink granules. The monocyte nucleus is lobulated and that of a metamyelocyte indented.
The monocyte needs to be differentiated from a neutrophilic metamyelocyte, a cell with a similar size and indented nucleus. The monocyte has a fine chromatin. The chromatin of the metamyelocyte is coarser and clumped. The cytoplasm of a monocyte is grey or light grey blue cytoplasm and fine azurophilic granules whereas the cytoplasm of a metamyelocyte has is pink with fine pink granules.
Typically lymphocytes are small (10-12μm) cells with a scanty agranular cytoplasm with a round slightly indented nucleus. About 10% of lymphocytes are larger (12-16μ), have a nucleus which has a slight less compact chromatin and azurophilic granules in the cytoplasm. These are known as large granular lymphocytes. Some of these are T supressor lymphocytes (Cd3+ Cd8+) while others are NK cells (Cd3 – CD8+). The picture above shows a large granular lymphocyte.