INTERPRETATION OF FRONTAL CHEST RADIOGRAPHS Adequacy Having made sure it is the correct radiograph, check the side marker and look for any details written or stamped on the film. This will tell you if the film is posteroanterior or anteroposterior. Assess the exposure, by looking at the midthoracic intervertebral discs and noting if they are just visible through the mediastinal density. In overexposed films all the intervertebral discs are seen and the radiograph appears generally blacker. In con- trast underexposure gives rise to poor definition of structures and boundaries. The film should show the lung apices and bases including the costophrenic recesses, the lateral borders of the ribs, and peripheral soft tissues. The right hemidiaphragm should reach the anterior end of the right sixth/seventh rib or the ninth/tenth rib poste- riorly on full inspiration. Poor inspiration (diaphragm higher than anterior fifth rib) affects the lower zone vessels such that they are compressed and appear more prominent. This in turn leads to vague lower zone shadowing. In addition, the heart appears enlarged because the diaphragms are high and the heart lies more horizontally. Alignment This is determined by looking at the relationship between the spinous processes of the upper thoracic vertebrae and the medial aspects of the clavicles.The ends of both clavi- cles should be equidistant from the central spinous process. As with adequacy, alignment of the patient to the X-ray can significantly alter the size and shape of the chest contents on the radiograph. For example, if the patient is rotated there is distortion of the mediastinal contours as well as inequality in the transradiancy of the hemithoraces. In addition to postural and rotational artefacts, remember the configuration of the patient’s chest wall can also give rise to abnormal appearances. For example, pectus excavatum can alter the size, shape, and position of the mediastinum, as well as produc- ing inequality in the transradiancy of the lungs. Bones The posterior, lateral, and anterior aspects of each rib must be examined in detail. This can be done by tracing out the upper and lower borders of the ribs from the posterior costochondral joint to where they join the anterior costal cartilage at the midclavicular line. The internal trabecula pattern can then be assessed. Finish assessing the bones by inspecting the visible vertebrae, the clavicles, scapulae and proximal humeri. However, for full assessment specific views must be obtained. Cartilage and joints Calcification in the costal cartilage is common in the elderly – similarly in the larynx. Occasionally the glenohumeral joints are seen on the chest X-ray. They may show either degenerative or inflammatory changes. Soft tissue The soft tissue can be considered in three parts. ● Mediastinum ● Lungs and diaphragm ● Extrathoracic soft tissues. ACUTE MEDICAL EMERGENCIES: THE PRACTICAL APPROACH 366 24-AcuteMed-24-cpp 28/9/2000 4:57 pm Page 366 Mediastinum The mediastinum normally occupies the centre of the chest radiograph and has a well defined margin.You should consider the upper, middle (hila), and lower (heart) parts of the mediastinum. Upper mediastinum Check the position of the trachea. This should be central. The upper left mediastinal shadow is formed by the left subclavian artery. This normally gives rise to a curved border which fades out where the vessels enter the neck. The left outer wall of the trachea is not visible in this area because the subclavian vessels separate the trachea from the aerated lung. Inferiorly, the left paratracheal region is inter- rupted by both the aortic knuckle and the main pulmonary artery with the space between the two being known as the ‘aortopulmonary window’. The aortic knuckle should be well defined. Middle mediastinum The hila shadows are produced mainly by the pulmonary arteries and veins. The major bronchi can be identified as air containing structures but the bronchial walls are com- monly only visible when seen end on. Though a contribution is made to these shadows by the hilar lymph nodes, they cannot be identified separately from the vascular shadows. The left hilum is usually higher than the right. Any lobulation of the hilar shadow, local expansion or increase in density compared with the opposite side indicates a central mass lesion. Central enlargement of the pul- monary arteries may mimic mass lesions but the vascular enlargement is usually bilat- eral, accompanied by cardiomegaly and forms a branching shadow. Lower mediastinum The overall position, size, and shape of the heart should be noted first. Normally the car- diac shadow can have a transverse diameter which is up to 50% of the transverse diame- ter of the chest on a posteroanterior film. Cardiomyopathy or pericardial effusion can both give rise to a globular heart shadow but further diagnostic clues are usually avail- able from the clinical history and examination. The heart borders can then be assessed. The heart silhouette should be sharp and single with loss of a clear border indicating neighbouring lung pathology. A double out- line suggests a pneumomediastinum/pneumopericardium. With a pneumomediastinum a translucent line can usually be seen to extend up into the neck and be accompanied by subcutaneous emphysema. Inspection of the heart is completed by checking for calcification (valves and peri- cardium) and retrocardiac abnormalities, e.g. hiatus herniae, increased density or the presence of foreign bodies. Lungs and diaphragm Lungs These are best assessed initially by standing back from the radiograph so that you can compare the overall size and transradiancy of both hemithoraces. A number of changes may be seen. Reduced volume The commonest cause of lung volume loss is lobar collapse. When complete, these give rise to dense white shadows in specific locations and are usually accompanied by hilar displacement, increased radiolucency in the remaining lobes and CHEST X-RAY INTERPRETATION 367 24-AcuteMed-24-cpp 28/9/2000 4:57 pm Page 367 reduction in the vascular pattern due to compensatory emphysema.When the collapse is incomplete, consolidation in the remaining part of the lobe is evident. Reduced density The transradiancy of both lungs should be equal and their outer edges should extend out to the ribs laterally and the diaphragm below. Any separation indicates that there is a pneumothorax.Within the normal lungs the only identifiable structures are blood vessels, end on bronchi and the interlobar fissures. Air trapping gives rise to increased translucency and flattening of the dome of the diaphragm. In extreme cases the mediastinum may be displaced to the contralateral side. Increased density There are several causes for an increase in pulmonary density. In con- solidation the density is restricted to either part or all of a pulmonary lobe as a result of the air being replaced with fluid. With segmental consolidation the density is rounded and the edges blurred. When the whole of the lobe is involved the interface with neigh- bouring soft tissues is lost. This can lead to alteration in the outline of the heart and diaphragm depending upon the location of the lobe (see earlier). Pleural fluid is seen initially as blunting of the costophrenic angle. As more accumu- lates the fluid level is easier to make out. However, if the patient is supine the fluid col- lects posteriorly and gives rise to a general ground-glass appearance on the affected side. Consequently, an effusion may be missed until it is large or the frontal and erect chest radiograph is carried out. Pulmonary oedema presents as generalised fluffy air space shadowing which can be accompanied by Kerley B lines due to interstitial lymphatic congestion. The position, configuration, and thickness of the fissures should also be checked – any- thing more than a hairline thickness should be considered abnormal. To visualise a fis- sure the X-ray beam needs to be tangential; therefore, only the horizontal fissure is evident on the frontal film, and then only in 50% of the population. It runs from the right hilium to the sixth rib in the axilla. The azygos fissure is seen in approximately 1% of the population.The oblique fissures are only identified on the lateral view. Diaphragm The diaphragm must be checked for position, shape, and clarity of the cardiophrenic and costophrenic angles.The outline of the diaphragm is normally smoothly arcuate with the highest point medial to the midline of the hemithorax. Lateral peaking, particularly on the right, suggests a subpulmonary effusion or a haemothorax in the appropriate clinical setting. In the vast majority of patients the right diaphragm is higher than the left. However, elevation of either side can result from pathology in the abdomen or damage to the phrenic nerve. In this situation the patient’s history will be very helpful in distinguishing between these possible causes. The upper surface of the diaphragm is normally clearly outlined by air in the lung except where it is in contact with the heart and pericardial fat. Loss of clarity may indi- cate collapse or consolidation of the lower lobe. It could also indicate diaphragmatic rupture. Extrathoracic soft tissue Start at the top with the neck and supraclavicular area, and continue down the lateral wall of the chest on each side. Note any foreign bodies and subcutaneous emphysema. The latter is often seen in the cervical region and appears as linear transradiancies along tissue planes. When gross it may interfere with the assessment of the underlying lung. Finally, check under the diaphragm for abnormal structures or free gas. ACUTE MEDICAL EMERGENCIES: THE PRACTICAL APPROACH 368 24-AcuteMed-24-cpp 28/9/2000 4:57 pm Page 368 Presence and position of any medical equipment The position and presence of any invasive medical equipment must be assessed while the radiograph is examined so that potential complications can be identified. A further chest X-ray should be performed after the placement of any of these devices in order to exclude or detect the above complications. Reassess commonly missed areas Once the system described above has been completed, it is important to reevaluate those areas where pathology is often overlooked.These include: ● the lung apices ● behind the heart shadow ● under the diaphragm ● peripheral soft tissues. Summary of the system for assessing frontal chest radiographs ● Assess the adequacy of the film Patient’s personal details Projection of the X-ray beam Exposure of the film Area of the chest on the film Degree of inspiration ● Assess the alignment of the film ● Assess the bones Extrathoracic Spine Shoulder Foreign bodies Air Under the diaphragm ● Assess the cartilage and joints ● Assess the soft tissue Mediastinum Upper Middle (hila) Lower (heart) Lungs and diaphragm Lungs Size Density Fissures Nodules and opacifications Diaphragm Position Shape Clarity of the angles Foreign bodies Air Under the diaphragm ● Reassess commonly missed areas of the film Apices Behind the heart Under the diaphragm Peripheral soft tissues CHEST X-RAY INTERPRETATION 369 24-AcuteMed-24-cpp 28/9/2000 4:57 pm Page 369 This Page Intentionally Left Blank CHAPTER 25 Haematological investigations OBJECTIVES After reading this chapter you will be able to: ● identify which haematological tests are useful in the acute medical patient ● describe the rational use of such tests ● use test results to aid further clinical management. INTRODUCTION A full blood count is probably the commonest laboratory investigation that is requested because it is a “routine test”.There is, however, no such commodity as a routine test and you should be able to justify requesting any investigation. A similar situation, though much less common, exists when requesting assessment of the components of the clotting cascade. It is, therefore, important that you critically appraise your requests and also interpret all the available information provided by, for example, a full blood count, and not just the haemoglobin, as often occurs. RULES When interpreting haematological results: ● Always request investigations and interpret results in light of clinical findings. ● Beware: – the isolated abnormality – bizarre results – results that do not fit with the clinical picture. ● If in doubt repeat the test. ● Always seek corroborative evidence from: – clinical findings – other test results. ● Always observe serial results for trends. 371 Reading: 30 minutes 25-AcuteMed-25-cpp 28/9/2000 4:58 pm Page 371 REVISION Many haematological disorders are identified by, or suggested by, an abnormality in the full blood count. The result usually relates to three major cell lines in peripheral blood: erythrocytes, leucocytes, and platelets. In addition there is a wealth of numerical infor- mation describing these cell lines that is often ignored – at the clinician’s peril.This infor- mation, generated by automatic haematology counters, should be used to the clinician’s advantage – hence the need for revision of some of the key cell count components. HAEMOGLOBIN LEVEL The normal levels of haemoglobin are 15 ± 2 g/dl (150 ± 20 g/l) for men and 14 ± 2 g/dl (140 ± 20 g/l) for women. In the acute medical patient a raised haemoglobin often indi- cates polycythaemia.This is commonly associated with chronic respiratory disease rather than the rare polycythaemia rubra vera. In contrast, the haemoglobin level may be low indicating anaemia. However, remember that in patients with acute blood loss the haemoglobin level may be normal initially, until either compensatory measures fail or haemodilution occurs. The red cell count is quoted by some laboratories, but this has little diagnostic value in the acute medical patient. However, the combination of haemoglobin and red cell count can be used to derive the mean cell haemoglobin (MCH).This gives a reliable indi- cation of the amount of haemoglobin per red cell and is measured in picograms (normal range 29.5 ± 2·5 pg).The mean cell haemoglobin concentration (MCHC) represents the concentration of haemoglobin in grams per decilitre (100 ml) of erythrocytes (normal range 33 ± 1·5 g/dl). This is obtained by dividing the haemoglobin concentration by the packed cell volume. A low mean cell haemoglobin concentration is due to a low haemo- globin content in the red cell mass and indicates deficient haemoglobin synthesis. Thus the red cells will appear pale (hypochromic). Remember that high mean cell haemoglo- bin concentrations do not occur in red cell disorders because the haemoglobin concen- tration is already near saturation point in normal red cells. The mean cell haemoglobin concentration, unlike the mean cell haemoglobin, assesses the degree of haemoglobini- sation of the red cells irrespective of their size and is useful in assessing the extent of under-haemoglobinisation. The packed cell volume (PCV or haematocrit) represents a proportion (by volume) of whole blood occupied by the red cells and is expressed as a percentage (normal range for men 47 ± 7, women 42 ± 5%).The packed cell volume or haematocrit is always elevated in polycythaemia irrespective of cause. However, this may only be relative when haemoconcentration occurs as a result of fluid loss producing a decrease in plasma volume.The packed cell volume is therefore reduced in the presence of excess extracellular fluid and raised in fluid depletion. The mean cell value (MCV) measured in femtolitres (normal range 85 ± 10 fl) indicates erythrocyte size. Thus, it is increased in patients with macrocytic disorders (e.g. vitamin B12/folate deficiency) and reduced in the presence of microcytes (e.g. iron deficiency anaemia). It is important to realise that red cell indices indicate the average size and degree of haemoglobinisation of red cells. They are, therefore, only of value if combined with a blood film examination that will augment the information about the relative uniformity of changes in either cell size or haemoglobin concentration. THE BLOOD FILM The benefits of the blood film have already been described. Some of the common terms used to describe cell morphology are listed in the box. ACUTE MEDICAL EMERGENCIES: THE PRACTICAL APPROACH 372 25-AcuteMed-25-cpp 28/9/2000 4:58 pm Page 372 RED CELL ABNORMALITIES Red cell abnormalities can be classified as alterations in either number or morphology. Alteration in number An increase in red cells is described as polycythaemia (see earlier). In contrast anaemia is described as diminished oxygen carrying capacity of the blood due to either a reduc- tion in the number of red cells or in the content of haemoglobin or both.This may be due to deficient red cell production and/or excessive loss. Although there is some overlap between these conditions this classification does provide a convenient way of considering this condition (see the next box). Deficient red cell production Iron deficiency anaemia secondary to: ● poor dietary intake ● malabsorption ● chronic blood loss Vitamin B12 or folic acid deficiency secondary to: ● pernicious anaemic ● malabsorption of vitamin B12 or folic acid ● pregnancy ● hypothyroidism ● vitamin C deficiency ● drug use including alcohol ● aplasia ● invasion of bone marrow by, e.g. leukaemia, Hodgkin’s lymphoma, myeloma ● toxic effects on erythroblasts, e.g. uraemia, chronic infections, and malignant disease Morphological terms on blood cell reports Red cells Pale cells Hypochromia indicating defective haemoglobinisation or haemoglobin synthesis Macrocytes Large cells, abnormal red cell production, premature release, megaloblastic erythropoiesis, haemolysis Anisocytes Variation in cell size Poikilocytes Variation in cell shape Schistocytes Burr cells Fragmented forms, usually indicate red cell trauma Sickle cells Sickling disorders White cells Hypersegmented Usually indicates vitamin B12 or folate neutrophils deficiency Left shift neutrophils Indicate that neutrophils are being prematurely released Toxic granulation Increased neutrophils Cytoplasmic granularity Usually associated with underlying infection Atypical lymphocytes Likely viral infection Blast cells Usually indicate leukaemia Platelets Clumping Often causing an artificially low platelet count HAEMATOLOGICAL INVESTIGATIONS 373 25-AcuteMed-25-cpp 28/9/2000 4:58 pm Page 373 An anaemia with a coexistent reduction in both white cells and platelets is referred to as pancytopenia. Alteration in morphology An anaemia with reduced mean cell volume, mean cell haemoglobin, and mean cell haemoglobin concentration, i.e. microcytic hypochromic anaemia, is highly suggestive of iron deficiency. Therefore a serum ferritin should be requested before treatment with iron is started. However, if there is coexistent thrombocytosis then this type of anaemia could indicate ongoing blood loss or inflammation. If none of these conditions are evi- dent then it is possible that the microcytic hypochromic picture is a manifestation of thalassaemia, which is rare in the United Kingdom. In contrast an anaemia with raised mean cell volume and mean cell haemoglobin is suggestive of a variety of conditions including a deficiency in vitamin B12 and/or folic acid, hypothyroidism, and alcohol use. An anaemia with normal mean cell volume, mean cell haemoglobin and mean cell haemoglobin concentration, i.e. a normochromic normocytic anaemia, can reflect chronic disease (e.g. inflammation, myeloma), acute blood loss or haemolysis. Haemolysis is usually associated with a normochromic normocytic anaemia although some of the red cells can be large due to the release of a large number of immature red cells, i.e. reticulocytes.The latter can also occur following haemorrhage or in response to treatment with iron, folic acid, and vitamin B12.The comment polychromasia (grey/blue tint to cells) is often recorded on the full blood count indicating a reticulocyte response. A formal count of these cells can also be done. Haemolytic anaemia is a term that describes a group of anaemias of differing cause, which are all characterised by abnormal destruction of red cells. The questions asked to identify the cause of haemolysis are shown in the box. These questions can be used to produce a “user frendly” classification of haemolytic anaemia as shown in the box. Three key questions in the diagnosis of haemolytic anaemia ● Is it an inherited or acquired disorder? ● Is the location of the abnormality within the red cells (intrinsic) or outside (extrinsic)? ● Are the red cells prematurely destroyed in the blood stream (intravascular) or outside in the spleen and liver (extravascular)? Excessive loss of red blood cells ● Haemorrhage ● Abnormal haemolysis ● Hypersplenism ● Drugs ACUTE MEDICAL EMERGENCIES: THE PRACTICAL APPROACH 374 25-AcuteMed-25-cpp 28/9/2000 4:58 pm Page 374 LABORATORY DIAGNOSIS OF HAEMOLYTIC ANAEMIA The most likely clue is a normochromic normocytic anaemia with prominent reticulo- cytes. Other laboratory results include: ● unconjugated hyperbilirubinanaemia (thus a lack of bilirubin in the urine). ● low haptoglobin (a glycoprotein that binds to free haemoglobin and is thus depleted in haemolysis). ● Haemoglobin and haemosiderin can be detected in the urine with intravascular haemolysis. Inherited disorders More specific tests will be requested after taking a comprehensive history as this is likely to provide clues to underlying inherited disorders.The presence of hereditary spherocy- tosis or elliptocytosis will be seen on the blood film. The thalassaemias are a heterogeneous group of disorders affecting haemoglobin syn- thesis; they will be diagnosed from the medical history, clinical examination, blood film, and haemoglobin electrophoresis to identify structural haemoglobin variants. In addi- tion, the presence of sickle cell syndromes will be diagnosed from the clinical history, in particular that of the family, and the presentation with haemolysis, vascular occlusive crises, and sequestration crises. Under these circumstances the blood film is likely to show the presence of sickle shaped cells. Haemoglobin electrophoresis may reveal an abnormal haemoglobin such as Hbss in sickle cell anaemia with no detectable haemo- globin A. The two common abnormalities of red cell metabolism resulting in haemolysis are glu- cose 6 phosphate dehydrogenase deficiency and pyruvate kinase deficiency. As well as the features of intravascular haemolysis described earlier, specific enzyme levels can also be measured to produce a definitive diagnosis. Acquired disorders Autoimmune haemolytic anaemia is a form of acquired haemolysis with a defect outside the red cell. The bone marrow produces structurally normal red cells. These are prema- turely destroyed by the production of an aberrant antibody targeted against one or more antigens on the red cell membrane. Once the autoantibody has bound with the antigen Classification of haemolytic anaemias ● Inherited disorders Red cell membrane hereditary spherocytosis hereditary elliptocytosis Haemoglobin thalassaemia syndromes sickle cell disorders Metabolic pathways glucose 6 phosphate dehydrogenase deficiency pyruvate kinase deficiency ● Acquired disorders Immune warm and cold autoimmune haemolytic anaemia Isoimmune rhesus or ABO incompatibility Non-immune and trauma valve prosthesis, microangiopathy, drugs, infection, chemicals, hypersplenism HAEMATOLOGICAL INVESTIGATIONS 375 25-AcuteMed-25-cpp 28/9/2000 4:58 pm Page 375 [...]... stress, eating or during the menstrual cycle The total leucocyte count is 7 ± 3 × 1 09/ l This comprises: ● ● ● ● ● neutrophils 2–7 × 1 09/ l (40–80% of total count) lymphocytes 1–3 × 1 09/ l (20–40% of total count) monocytes 0·2–1 × 1 09/ l (2–10% of total count) eosinophils 0·04–0·4 × 1 09/ l (1–6% of total count) basophils 0·02–0·1 × 1 09/ l (< 2% of total count) DISORDERS OF LEUCOCYTES There are many conditions that... 20 × 1 09/ l COAGULATION The physiological pathway of blood coagulation is an interlinked cascade of factors which most doctors learn for examinations The basic principles are three activation pathways: intrinsic, extrinsic, and alternative, which have a final common pathway Individual components of these pathways are shown in Figures 25.1 and 25.2 Figure 25.1 Clotting pathways 3 79 ACUTE MEDICAL EMERGENCIES: ... haematological investigations are required in the acutely ill medical patient Much of the information available is often underused; therefore a thorough understanding of the morphology and normal values of, in particular, red cells is extremely useful A blood film is an underused investigation that can yield significant relevant information in the acute medical setting These initial investigations, combined... then falls 4 If oxygen is available, add via the nipple at 12–15 l/min 393 ACUTE MEDICAL EMERGENCIES: THE PRACTICAL APPROACH Figure 27.3 Haerdal pocket mask OROTRACHEAL INTUBATION Equipment ● Laryngoscope: most commonly with a curved (Macintosh) blade ● Tracheal tubes: females 7·5–8·0 mm internal diameter, 21 cm long males 8·0 9 0 mm internal diameter, 23 cm long ● Syringe, to inflate the cuff ● Catheter... placement of the tube 395 ACUTE MEDICAL EMERGENCIES: THE PRACTICAL APPROACH Manoeuvres to assist with intubation Occasionally, when the larynx is very anterior, direct pressure on the thyroid cartilage by an assistant may aid visualisation of the cords (not to be confused with cricoid pressure) However, despite this manoeuvre, in a small percentage of patients only the very posterior part of the cords (or... Needle cricothyroidotomy Equipment ● ● ● ● ● Venflons 12–14 gauge Jet insufflation equipment Oxygen tubing with either a threeway tap or a hole cut in the side 20 ml syringe Mannikin/sheep’s larynx 399 ACUTE MEDICAL EMERGENCIES: THE PRACTICAL APPROACH Procedure 1 Place the patient supine with the head slightly extended 2 Identify the cricothyroid membrane as the recess between the thyroid cartilage (Adam’s... extracellular fluid volume In contrast hyponatraemia with expansion of the extracellular volume occurs with cardiac, renal, and liver failure The urine sodium can provide further clues, in particular, in the 385 ACUTE MEDICAL EMERGENCIES: THE PRACTICAL APPROACH patient who is hyponatraemic with an increased extracellular volume where the urine sodium is usually less than 10 mmol/l (except in renal failure)... airway is inserted 2 Insert the airway into the mouth either (i) “upside down” (concave uppermost) as far as the junction between the hard and soft palates and rotate through 180º or (ii) use 391 ACUTE MEDICAL EMERGENCIES: THE PRACTICAL APPROACH a tongue depressor or the tip of a laryngoscope blade to aid insertion of the airway “the right way up” under direct vision 3 Insert so that the flange lies... tumour or marrow fibrosis Specific deficiencies of vitamin B12 and folic acid Peripheral sequestration/hypersplenism Shock Severe infection 377 ACUTE MEDICAL EMERGENCIES: THE PRACTICAL APPROACH Disorders of lymphocytes Raised numbers (lymphocytosis, i.e > 4 × 1 09/ l) Reduced numbers (lymphopenia) Viral infection, especially glandular fever* Chronic lymphatic leukaemia Typhoid fever Brucellosis Corticosteroids... Tests for the assessment of coagulation In most acute medical situations, an assessment of the coagulation cascade only requires: ● prothrombin time – a measure of the function of the extrinsic pathway ● activated partial thromboplastin time – assesses the intrinsic pathway ● assessments of fibrinolysis, e.g fibrinogen level, fibrin degradation product level or D-dimer quantitation – are often used as markers . gas. ACUTE MEDICAL EMERGENCIES: THE PRACTICAL APPROACH 368 24-AcuteMed-24-cpp 28 /9/ 2000 4:57 pm Page 368 Presence and position of any medical equipment The position and presence of any invasive medical. plasmin that is produced from plas- ACUTE MEDICAL EMERGENCIES: THE PRACTICAL APPROACH 380 Figure 25.2 The endogenous system for fibrin digestion. 25-AcuteMed-25-cpp 28 /9/ 2000 4:58 pm Page 380 minogen. the heart Under the diaphragm Peripheral soft tissues CHEST X-RAY INTERPRETATION 3 69 24-AcuteMed-24-cpp 28 /9/ 2000 4:57 pm Page 3 69 This Page Intentionally Left Blank CHAPTER 25 Haematological