Chapter 21: Haematological procedures
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Sources: Adapted from Bain ([7]), Hoffbrand and Moss ([51]), Hughes‐Jones et al. ([54]), Provan et al. ([95]), Turgeon ([112]).
Anatomy and physiology
Bone marrow
The maturation of blood cells is termed haematopoiesis (Davē and Koury [27]) and takes place in the bone marrow. At 5–9 months of fetal life, the bone marrow, liver and spleen produce the cellular components of blood. At birth, the marrow of all bones is involved in haematopoiesis. During childhood, there is some replacement of the haematopoietic tissue (red marrow) with fatty tissue (yellow marrow). In adults, the only sites of haematopoiesis are bones such as the pelvis and sternum (Yarbro et al. [116]). Yellow marrow has the ability to revert to haematopoietic tissue in certain circumstances such as haemolytic anaemia (Davē and Koury [27]).
Stem cells
All mature blood cells originate from one precursor cell called a stem cell. The stem cell has the ability for unlimited self‐renewal (can produce more stem cells) and differentiation (can develop into any of the mature blood cell types) (Figure 21.1).
Figure 21.1 The stem cell and the blood cells that arise from it. Source: Dougherty and Lister ([35]).
The self‐renewal and differentiation of stem cells are regulated by acidic glycoprotein molecules called haematopoietic growth factors (Traynor [110]). Some growth factors are found naturally in the plasma but others are only detectable following an inflammatory event or other stimulus (Hoffbrand and Moss [51]). Growth factors include granulocyte‐colony stimulating factor (G‐CSF), erythropoietin and thrombopoietin (Traynor [110]).
The first step in the differentiation process is a division of the stem cell into two main cell lineages: myeloid and lymphoid. The myeloid progenitor cell divides into red blood cells, platelets, granulocytes (neutrophils, eosinophils and basophils) and monocytes (macrophages). The lymphoid progenitor cell matures into lymphocytes (T and B). Lymphocytes, granulocytes and monocytes are all white cells (Bondurant et al. [15]). The main functions of the blood cells and the haematological values for normal adults are listed in Table 21.1.
Table 21.1 The main function of blood cells and the haematological values for normal adults
| Blood cell type and function | Haematological value | Illustration |
|---|---|---|
Red blood cells (erythrocytes)
Transport oxygen from the lungs to the tissues and return carbon dioxide from the tissues to be expelled by the lungs | Men: 15 ± 2 g/dL
Women: 14 ± 2 g/dL | |
Platelets (thrombocytes)
Form mechanical plugs during the normal haemostatic response to vascular injury | 130–400 × 109/L | |
White blood cells (leucocytes)
A group of diverse cells that work together to protect the body from disease and to provide immunity | 7.0 ± 3.0 × 109/L | |
White blood cell differential
Neutrophil: Attracted to sites of infection (chemotaxis); ingests micro‐organisms (phagocytosis) and destroys them | 2.0–7.0 × 109/L | |
| Eosinophil: Same function as the neutrophil; in addition, helps control parasitic infections; has a role in allergic responses | 0.04–0.4 × 109/L | |
| Basophil: Has a role in immediate hypersensitivity reactions, allergic and inflammatory responses and in the control of parasitic infections | 0.02–0.1 × 109/L | |
T lymphocyte: Attacks cells bearing foreign antigens and antibody‐coated cells; can help or suppress B cells (part of cell‐mediated immunity)
B lymphocyte: Matures into a plasma cell, which secretes antibodies (humoral immunity)
Natural killer (NK) lymphocyte: Attacks foreign cells and tumour cells (part of cell‐mediated immunity) | 1.0–3.0 × 109/L | |
| Monocyte (differentiates to macrophage in tissues): Has a role in chemotaxis, phagocytosis, killing of some micro‐organisms (fungi and mycobacteria), release of IL‐1 and TNF which stimulate bone marrow stromal cells to produce GM‐CSF, G‐CSF, M‐CSF and IL‐6 | 0.2–1.0 × 109/L |
| G‐CSF, granulocyte‐colony stimulating factor; GM‐CSF, granulocyte‐macrophage colony stimulating factor; IL, interleukin; M‐CSF macrophage colony stimulating factor; TNF, tumour necrosis factor. |
Plasma
Plasma gives blood its liquid property to allow it to flow through the vascular system. If the cellular components of whole blood were allowed to sediment in a test tube, around 54% of the volume would be the straw‐coloured plasma (Traynor [110]). Plasma consists of water, plasma proteins (e.g. fibrinogen, albumin, globulins), electrolytes (e.g. sodium, potassium, chloride) and metabolites (e.g. urea, creatinine, cholesterol). The functions of these elements include clotting, maintaining blood pressure, controlling plasma viscosity, antibody formation and regulating intra/extracellular pressure.
