Manual of basic techniques for a health laboratory - libdoc.who.int

9. Haematology 315Fig. 9.104 Mixing the blood and sodium metabisulfite solution9.11.3 Method1. Place a small drop of capillary blood (about 4mm diameter)in the centre of a slide (see Fig. 9.65).2. Add an equal-sized drop of sodium metabisulfitesolution.3. Mix carefully with the corner of a slide (Fig. 9.104). Coverwith a coverslip, making sure that no air bubbles form.4. Place the slide in a Petri dish that has wet filter-paper inthe bottom. Support the slide on two sticks (Fig. 9.105).Wait 30 minutes before examining the slide.Note: When using a reducing reagent such as sodiummetabisulfite it is not necessary to seal the preparation.Fig. 9.105 Incubating the slide in a Petri dish9.11.4 Microscopic examinationExamine the slide under the microscope using the ¥ 40objective.Negative resultThe erythrocytes remain round (Fig. 9.106).If the test is negative, re-examine the slide after a further 30minutes, then after 2 hours and after 24 hours.Fig. 9.106 Test for sickle-cell anaemia: negativeresultPositive resultThe erythrocytes become sickle-shaped or banana-shaped(Fig. 9.107 (a)), often with spikes (Fig. 9.107 (b)).It is important to examine several parts of the preparation,as sickling can occur more quickly in one part than in another.Do not mistake normal erythrocytes lying on their side orcrenated cells for sickle cells.Fig. 9.107 Test for sickle-cell anaemia: positiveresulta: Sickle-shaped erythrocytes; b: sickleshapederythrocytes with spikes.