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286 Manual of basic techniques for a health laboratory erythrocyte haemoglobin concentration may be as high as 380g/l (haemoglobin(Fe) 23.6mmol/l), but it never exceeds these values. The mean erythrocyte haemoglobin concentration is usually called the “mean corpuscular haemoglobin concentration” (MCHC). It can also be expressed as a percentage. This is calculated by dividing the haemoglobin concentration of the blood in grams per 100ml by the packed cell volume as a percentage and multiplying by 100. Example: haemoglobin concentration = 15.0g/100ml packed cell volume = 43% MCHC = (15.0/43) ¥ 100 = 35%. In this system, the reference range is 32–37%. The MCHC never exceeds 38%. If such a result is obtained, the test should be repeated. 9.4.2 Macro-scale method Principle The blood (mixed with anticoagulant) is placed in a graduated tube and centrifuged to pack the erythrocytes. The level of the column of erythrocytes is then read directly in the graduated tube (Fig. 9.36). Materials and reagents (Fig. 9.37) ● ● ● ● Centrifuge Special graduated tubes (Wintrobe tubes), 9.5cm long with a 0.6-cm bore, calibrated from 0 to 100 Long fine capillary Pasteur pipette (long enough to reach the bottom of the tube) with rubber teat Anticoagulant — EDTA dipotassium salt, 10% solution (reagent no. 22) or Wintrobe solution (reagent no. 65). Fig. 9.36 Principle of the macro scale for estimating the erythrocyte volume fraction Method Collection of specimens 1. Collect a venous blood specimen as described in section 9.2 and add it to a graduated tube containing anticoagulant (see above). 2. Using the capillary pipette, fill the graduated tube with blood up to the 100 mark, making sure that no air bubbles form (Fig. 9.38). Fig. 9.37 Materials for estimating the erythrocyte volume fraction using the macro scale Fig. 9.38 Using a capillary pipette to fill a graduated tube with blood
9. Haematology 287 Measurement technique 1. Place the graduated tubes in the centrifuge and centrifuge for 30 minutes at 2300g. If the rotor arm of the centrifuge (measured from the axis of rotation to the base of the bucket holding the tube) is 15cm long, 3600rpm will be needed to attain this force; with a 20-cm arm 3100rpm will be needed. Important: a force of less than about 2300g will give a false result. 2. Read the level at which the erythrocytes meet the layer of leukocytes (Fig. 9.39). Make sure that the correct set of graduations is being used, upwards towards the 100 mark. The figure obtained is a percentage (the “packed cell volume”); divide by 100 to obtain the erythrocyte volume fraction. Fig. 9.39 Measuring the packed cell volume Results See page 282. 9.5 Estimation of the erythrocyte number concentration The number of erythrocytes contained in 1 litre of blood is called the erythrocyte number concentration. (In traditional units, it is expressed as the number of erythrocytes per cubic millimetre and is called the erythrocyte or red cell “count”.) Accurate methods for counting erythrocytes require an electronic counter system. Unfortunately, such instruments are often not available in peripheral laboratories. A simple but far less accurate method uses a counting chamber in which erythrocytes are counted under the microscope. However, this method is of such low precision that it should not be used. It is recommended instead that the erythrocyte volume fraction (see section 9.4) or the haemoglobin concentration (see section 9.3) is measured and the erythrocyte number concentration calculated. Reference range Table 9.7 shows the reference ranges for different age groups. High values Patients who are dehydrated or have polycythaemia will have high erythrocyte number concentrations. Low values Patients with anaemia caused by insufficient production, loss or haemolysis of erythrocytes will have low erythrocyte number concentrations. Note: Anaemia is a clinical syndrome that has many different underlying causes. The clinical picture is determined by the extent and duration of anaemia. The Table 9.7 Normal erythrocyte number concentrations, by age group Age group Erythrocyte number concentration SI units (per litre) Traditional units (per mm 3 ) Newborn infants 5.0–7.0 ¥ 10 12 5.0–7.0 ¥ 10 6 Infants (1–6 months) 3.8–5.9 ¥ 10 12 3.8–5.9 ¥ 10 6 Children (4 years) 3.8–5.4 ¥ 10 12 3.8–5.4 ¥ 10 6 Women 4.0–5.4 ¥ 10 12 4.0–5.4 ¥ 10 6 Men 4.5–6.2 ¥ 10 12 4.5–6.2 ¥ 10 6
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M A N U A L O F B A S I C TECHNIQUE
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Contents i Manual of basic techniqu
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Contents iii Contents Preface x 1.
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Contents v 4.2.1 Collection of spec
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Contents vii PART III 231 7. Examin
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Contents ix 10.1.3 Method 322 10.1.
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1. Introduction 1 1. Introduction 1
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1. Introduction 3 The following sec
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1. Introduction 5 Table 1.4 SI deri
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1. Introduction 7 Table 1.5 (cont.)
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2. Setting up a peripheral health l
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3. General laboratory procedures 53
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4. Parasitology 103 Part II
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4. Parasitology 105 4.Parasitology
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4. Parasitology 107 4.2 Examination
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4. Parasitology 109 colourless, red
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4. Parasitology 111 Table 4.3 Patho
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4. Parasitology 113 Fig. 4.13 Invas
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4. Parasitology 115 Motility: eithe
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4. Parasitology 117 Rapid Field sta
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4. Parasitology 119 Fig. 4.24 Featu
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4. Parasitology 121 Identification
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4. Parasitology 123 Measurement Acc
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4. Parasitology 125 Shape: round or
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4. Parasitology 127 ● ● ● The
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4. Parasitology 129 Fig. 4.39 Terms
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4. Parasitology 131
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4. Parasitology 133 Fig. 4.42 Ancyl
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4. Parasitology 135 Dipylidium cani
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4. Parasitology 137 Fig. 4.59 Trans
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4. Parasitology 139 Fig. 4.66 Heter
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4. Parasitology 141 Shell: smooth,
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4. Parasitology 143 Fig. 4.79 Filli
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4. Parasitology 145 These granules
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4. Parasitology 147 Fig. 4.92 Adult
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4. Parasitology 149 Fig. 4.97 Featu
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4. Parasitology 151 Fig. 4.101 Schi
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4. Parasitology 153 Method Preparat
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4. Parasitology 155 2. Using the sp
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4. Parasitology 157 differentiated
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4. Parasitology 159 5. Add to the t
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4. Parasitology 161 Method Collecti
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4. Parasitology 163 Procedure for o
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4. Parasitology 165 Table 4.8 Chara
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4. Parasitology 167 Method 1. Colle
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4. Parasitology 169 7. Remove the s
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4. Parasitology 171 Cephalic space
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4. Parasitology 173 Table 4.10 Geog
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4. Parasitology 175 Fig. 4.132 Coll
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4. Parasitology 177 1. Allow the th
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4. Parasitology 179 Table 4.11 Comp
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4. Parasitology 181 Table 4.12 (con
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4. Parasitology 183 African trypano
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4. Parasitology 185 Fig. 4.144 Twis
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4. Parasitology 187 Fig. 4.150 Usin
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4. Parasitology 189 The above mater
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4. Parasitology 191 Fig. 4.158 Appl
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4. Parasitology 193 clinical sympto
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4. Parasitology 195 Examination of
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5. Bacteriology 197 5. Bacteriology
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5. Bacteriology 199 5.2.4 Fixation
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5. Bacteriology 201 Fig. 5.14 “Ac
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5. Bacteriology 203 Table 5.2 Repor
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5. Bacteriology 205 ● Parasites:
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5. Bacteriology 207 Throat specimen
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5. Bacteriology 209 Other bacteria
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5. Bacteriology 211 5.6.3 Microscop
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5. Bacteriology 213 Fig. 5.28 Sperm
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5. Bacteriology 215 3. Load an impr
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5. Bacteriology 217 Fig. 5.34 Vibri
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5. Bacteriology 219 2. Remove the s
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5. Bacteriology 221 5.12.2 Method C
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5. Bacteriology 223 Fig. 5.43 Trans
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6. Mycology 1 6.1 Examination of sk
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6. Mycology 227 6.2.1 Materials and
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6. Mycology 229 Fig. 6.8 Transferri
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232 Manual of basic techniques for
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370 Index BI, see Bacteriological i
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372 Index Dark-field microscopy 64,
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374 Index Formaldehyde-ether sedime
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376 Index Labelling (continued) spe
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378 Index Open two-pan balances 67-
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380 Index Reference ranges (continu
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382 Index Strongyloides stercoralis
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384 Index Venous blood collection 2
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This manual provides a practical gu
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